Abstract:

Provided is a microminiaturized zoom optical system capable of
sufficiently correcting aberration. The zoom optical system (100)
includes a first lens group (101) having a negative optical power, a
second lens group (102) having a positive optical power, and a third lens
group (103) having a positive or negative optical power in this order
from the object side. The zoom optical system is configured in such a
manner that the interval between the first lens group (101) and the
second lens group (102) is decreased in zooming from the wide angle end
to the telephoto end. A positive lens element in the third lens group
(103) or in a lens group closer to the image side than the third lens
group (103) satisfies the following conditional expression:
vp<40
where vp is the minimum value of the Abbe number of the positive lens
element.

Claims:

1. A zoom optical system including a first lens group having a negative
optical power, a second lens group having a positive optical power, and a
third lens group having a positive or negative optical power in this
order from an object side, the zoom optical system being configured in
such a manner that an interval between the first lens group and the
second lens group is decreased in zooming from a wide angle end to a
telephoto end, whereina positive lens element in the third lens group or
in a lens group closer to an image side than the third lens group
satisfies the following conditional expression (1):vp<40 (1)where vp
is a minimum value of the Abbe number of the positive lens element.

2. The zoom optical system according to claim 1, whereinthe positive lens
element having the Abbe number satisfies the following conditional
expression (2):Npg>1.7 (2)where Npg is a refractive index of the
positive lens element with respect to d-ray.

3. The zoom optical system according to claim 1, whereinthe positive lens
element having the Abbe number is made of a resin material, and satisfies
the following conditional expression (3):Npp>1.55 (3)where Npp is a
refractive index of the positive lens element made of the resin material
with respect to d-ray.

4. The zoom optical system according to claim 1, whereinthe positive lens
element having the Abbe number has at least one aspherical surface.

5. The zoom optical system according to claim 1, whereinthe second lens
group satisfies the following conditional expression
(4):0.7<f2/fw<2.0 (4)where f2 is a composite focal length of the
second lens group, and fw is a composite focal length of the entirety of
the zoom optical system at the wide angle end.

6. The zoom optical system according to claim 1, whereinthe zoom optical
system satisfies the following conditional expressions (5) and
(6):0<αw<30 (5)|αw-.alpha.t|<20 (6)where
αw is an angle (deg) of a principal ray, at a maximum image height,
of incident rays onto an imaging surface with respect to a normal to an
imaging plane at the wide angle end, and αt is an angle (deg) of
the principal ray, at the maximum image height, of the incident rays onto
the imaging surface with respect to the normal to the imaging plane at
the telephoto end, based on a premise that the angle of the principal ray
in the case where an exit pupil position is on the object side with
respect to the imaging plane is in a plus direction.

7. The zoom optical system according to claim 1, whereinthe zoom optical
system is constituted merely of the first lens group, the second lens
group, and the third lens group, andthe third lens group is constituted
of a positive lens element.

8. The zoom optical system according to claim 7, whereinthe third lens
group is fixed in zooming from the wide angle end to the telephoto end.

9. The zoom optical system according to claim 1, whereinthe third lens
group has a negative optical power, andthe zoom optical system includes a
fourth lens group which is arranged on the image side of the third lens
group and which has a positive optical power.

10. The zoom optical system according to claim 9, whereinthe positive lens
element having the Abbe number is included in the fourth lens group.

11. The zoom optical system according to claim 9, whereinthe fourth lens
group is constituted of a positive lens element.

12. The zoom optical system according to claim 9, whereinthe fourth lens
group is fixed in zooming from the wide angle end to the telephoto end.

13. The zoom optical system according to claim 9, whereinthe first lens
group is fixed in zooming from the wide angle end to the telephoto end.

14. The zoom optical system according to claim 1, whereinthe third lens
group has a positive optical power, andthe zoom optical system includes a
fourth lens group which is arranged on the image side of the third lens
group and which has a negative optical power.

15. The zoom optical system according to claim 14, whereinthe positive
lens element having the Abbe number is included in the third lens group.

16. The zoom optical system according to claim 14, whereinthe third lens
group is constituted of a positive lens element.

17. The zoom optical system according to claim 14, whereinthe fourth lens
group is fixed in zooming from the wide angle end to the telephoto end.

18. The zoom optical system according to claim 14, whereinthe first lens
group is fixed in zooming from the wide angle end to the telephoto end.

19. The zoom optical system according to claim 1, whereinthe second lens
group is constituted of a positive lens element and a negative lens
element in this order from the object side, and satisfies the following
conditional expression (7):0.7<|f2n/f2p|<1.8 (7)where f2n is a
focal length of the negative lens element in the second lens group, and
f2p is a focal length of the positive lens element in the second lens
group.

20. The zoom optical system according to claim 1, further comprising an
aperture stop on the object side of the second lens group, whereinthe
aperture stop has a fixed aperture diameter.

21. The zoom optical system according to claim 1, whereinthe positive lens
element having the Abbe number is a meniscus lens element convex to the
object side.

22. The zoom optical system according to claim 1, whereinan image-side
lens surface of the positive lens element having the Abbe number is
aspherical, andthe image-side lens surface of the positive lens element
satisfies the following conditional expression
(8):0.05<|ΔZpi/di|<0.25 (8)where ΔZpi is an amount of
aspherical sag, at a maximum effective radius, of the image-side lens
surface of the positive lens element having the Abbe number, and di is
the maximum effective radius of the image-side lens surface of the
positive lens element having the Abbe number.

23. The zoom optical system according to claim 1, whereinthe positive lens
element having the Abbe number satisfies the following conditional
expression (9):1<fp/fw<8 (9)where fp is a focal length of the
positive lens element having the Abbe number.

24. The zoom optical system according to claim 1, whereinthe first lens
group is constituted of a biconcave lens element or a negative meniscus
lens element convex to the object side, and of a positive meniscus lens
element convex to the object side in this order from the object side.

25. The zoom optical system according to claim 1, whereinfocusing from an
infinite object distance to a close object distance is performed by
moving the first lens group to the object side.

26. The zoom optical system according to claim 1, whereinfocusing from an
infinite object distance to a close object distance is performed by
moving the third lens group or the lens group closer to the image side
than the third lens group to the object side.

27. The zoom optical system according to claim 1, whereinthe second lens
group includes a cemented lens element.

28. The zoom optical system according to claim 1, whereinthe first lens
group includes a cemented lens element.

29. An imaging lens device, comprising:the zoom optical system of claim 1,
whereinthe zoom optical system is so configured as to form an optical
image of a subject on a predetermined image forming plane.

30. A digital apparatus, comprising:an image sensor, provided with a light
receiving surface, for converting an optical image of a subject into an
electric signal;an imaging lens device including the zoom optical system
of claim 1, the zoom optical system being adapted to form the optical
image of the subject on the light receiving surface of the image sensor:
anda controller for causing the imaging lens device and the image sensor
to perform at least one of still image shooting and moving image shooting
for the subject, whereinthe zoom optical system in the imaging lens
device is mounted in such a manner that the optical image of the subject
is formed on a light receiving surface of the image sensor.

31. The digital apparatus according to claim 30, whereinthe digital
apparatus is a mobile terminal device.

Description:

TECHNICAL FIELD

[0001]The present invention relates to a zoom optical system constituted
of lens groups for zooming by changing the interval between the lens
groups in the optical axis direction, an imaging lens device incorporated
with the zoom optical system, and a digital apparatus loaded with the
imaging lens device, and more particularly to a zoom optical system or a
like device adapted for miniaturization.

BACKGROUND ART

[0002]In recent years, mobile phones or PDAs (Personal Digital Assistants)
have been widespread. Also, the specifications in which a compact digital
still camera unit or a compact digital video unit is incorporated in the
mobile phone or the PDA have been generalized. In a digital apparatus
such as the mobile phone or the PDA, a small-sized image sensor with a
low pixel number, as compared with an independent product such as a
digital still camera, and an imaging lens device provided with a single
focus optical system constituted of one to three plastic lens elements
are generally used, in view of severe constraints regarding the size or
cost of the digital apparatus.

[0003]Since the magnification of the single focus optical system is
substantially equivalent to visual magnification, an object to be
photographed is limited to the one located near a photographer. Under the
current rapid development of high-pixel, high-resolution image sensors,
there is a demand for a compact zoom optical system that is compatible
with a high-pixel image sensor, and is loadable in a mobile phone or a
like device capable of photographing a subject remotely away from a
photographer.

[0004]For instance, patent document 1 proposes an arrangement directed to
a three-component zoom optical system of negative-positive-positive
arrangement which is constituted of a first lens group having a negative
optical power, a second lens group having a positive optical power, and a
third lens group having a positive optical power in this order from the
object side, wherein the total thickness of the optical system is reduced
when a lens barrel is collapsed. Also, patent document 2 discloses a
four-component zoom optical system of negative-positive-positive-positive
arrangement which is constituted of lens groups having a negative optical
power, a positive optical power, a positive optical power, and a positive
optical power in this order from the object side, wherein productivity of
an aspherical negative lens element in the first lens group is improved
by properly selecting a glass material for the aspherical negative lens
element.

[0005]It is difficult to employ the lens barrel collapsible structure as
recited in patent document 1 to a mobile phone or a like device, because
an impact resistance required for the mobile phone or a like device is
high. Accordingly, the optical system proposed in patent document 1 has
an unduly long entire length in use. Also, the second lens group is
constituted of three or more lens elements, and the total number of lens
elements is as large as six to eight. Therefore, miniaturization has not
been completely accomplished in the optical system disclosed in patent
document 1. In the zoom optical system recited in patent document 2, the
power of the second lens group is weak, and the optical system is not
compact because of a large moving amount. In addition to these drawbacks,
the number of lens elements is as large as seven. In light of these
drawbacks, it is difficult to mount the zoom optical system recited in
patent document 2 in a mobile phone or a like device.

[0006]The zoom optical systems in patent documents 1 and 2 employ a
negative dominant optical system, in which the first lens group closest
to the object side has a negative optical power. In the negative dominant
optical system, the second lens group primarily serving as an element for
zooming is required to have an extremely strong optical power in
microminiaturizing the optical system. In this case, particularly at a
telephoto end, magnification chromatic aberration resulting from an
increase in optical power of the second lens group is unduly increased,
which may lower the contrast in the periphery of a captured image, and
resultantly cause image degradation.

[0009]In view of the above conventional disadvantages, it is an object of
the present invention to provide a compact i.e. microminiaturized zoom
optical system that enables to obtain a high-quality image with respect
to the entirety of a captured image by sufficiently correcting
magnification chromatic aberration while maximally suppressing a moving
amount of lens groups for zooming, as well as an imaging lens device
incorporated with the zoom optical system, and a digital apparatus loaded
with the imaging lens device.

[0010]A zoom optical system according to an aspect of the invention
includes a first lens group having a negative optical power, a second
lens group having a positive optical power, and a third lens group having
a positive or negative optical power in this order from an object side.
The zoom optical system is configured in such a manner that an interval
between the first lens group and the second lens group is decreased in
zooming from a wide angle end to a telephoto end, wherein a positive lens
element in the third lens group or in a lens group closer to an image
side than the third lens group satisfies the following conditional
expression (1):

vp<40 (1)

where vp is a minimum value of the Abbe number of the positive lens
element.

[0011]In the above arrangement, the zoom optical system is configured into
a negative dominant optical system, in which the first lens group closest
to the object side has a negative optical power. This enables to promptly
alleviate emission of light rays incident from the object side with a
large angle by the negative optical power of the first lens group. This
is advantageous in reducing the entire length of the optical system or
the diameter of the forwardmost lens element. Also, in the negative
dominant arrangement, increase of error sensitivity can be suppressed
despite miniaturization of the optical system. These advantages are
particularly increased in a zoom lens device whose zoom ratio is about
two to three times.

[0012]If, however, miniaturization of the optical system further
progresses, the optical power required for the individual lens elements
constituting the second lens group in the aforementioned lens arrangement
is increased. As a result, magnification chromatic aberration at the
telephoto end may be unduly increased. In view of this, the positive lens
element in the third lens group or in the lens group closer to the image
side than the third lens group is made of a high dispersive material
having the Abbe number satisfying the aforementioned conditional
expression (1) to correct the aberration. If the Abbe number is over the
upper limit in the conditional expression (1), correction of
magnification chromatic aberration by the positive lens element is
insufficient, which may lower the contrast, and resultantly cause image
degradation.

[0013]The above arrangement of the invention enables to miniaturize the
zoom optical system as a negative dominant arrangement, and sufficiently
correct magnification chromatic aberration or a like drawback in the
second lens group, which may be involved in miniaturizing or
microminiaturizing the zoom optical system, by optimizing the Abbe number
of the positive lens element in the third lens group or in the lens group
closer to the image side than the third lens group. The arrangement is
advantageous in providing a satisfactorily miniaturized zoom optical
system whose aberration is desirably corrected in the entire zoom range
in a zoom optical system with a certain zoom ratio, particularly, in a
zoom optical system with a zoom ratio of about two to three times.

[0014]An imaging lens device according to another aspect of the invention
includes the aforementioned zoom optical system, wherein the zoom optical
system is so configured as to form an optical image of a subject on a
predetermined image forming plane.

[0015]A digital apparatus according to yet another aspect of the invention
includes the aforementioned imaging lens device, an image sensor for
converting the optical image into an electric signal, and a controller
for causing the imaging lens device and the image sensor to perform at
least one of still image shooting and moving image shooting for the
subject, wherein the zoom optical system in the imaging lens device is so
configured as to form the optical image of the subject on a light
receiving surface of the image sensor.

[0016]The aforementioned arrangements of the invention enable to realize a
compact, high-resolution, and zoomable imaging lens device that is
mountable in a mobile phone, a personal digital assistant, or a like
device, as well as a digital apparatus loaded with the imaging lens
device.

[0017]These and other objects, features and advantages of the present
invention will become more apparent upon reading the following detailed
description along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a diagram schematically showing an arrangement of a zoom
optical system to which an embodiment of the invention is applied.

[0019]FIG. 2 is a diagram showing a definition on an amount of aspherical
sag.

[0020]FIG. 3 is a diagram showing a definition on an incident angle of a
principal ray with respect to an imaging plane.

[0021]FIGS. 4A and 4B are diagrams showing an external appearance of a
camera phone loaded with a zoom optical system embodying the invention,
wherein FIG. 4A shows an operating surface of the camera phone, and FIG.
4B shows a back surface of the camera phone.

[0022]FIG. 5 is a functional block diagram showing a functional part
relating to an imaging operation to be executed by a mobile phone, as an
example of a digital apparatus loaded with the zoom optical system
embodying the invention.

[0023]FIG. 6 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 1 of the invention.

[0024]FIG. 7 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 2.

[0025]FIG. 8 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 3.

[0026]FIG. 9 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 4.

[0027]FIG. 10 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 5.

[0028]FIG. 11 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 6.

[0029]FIG. 12 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 7.

[0030]FIG. 13 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 8.

[0031]FIG. 14 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 9.

[0032]FIG. 15 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 10.

[0033]FIG. 16 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 11.

[0034]FIG. 17 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 12.

[0035]FIG. 18 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 13.

[0036]FIG. 19 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 14.

[0037]FIG. 20 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 15.

[0038]FIG. 21 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 16.

[0039]FIG. 22 is a cross-sectional view showing an optical path diagram at
a wide angle end in a zoom optical system as Example 17.

[0040]FIG. 23 is a cross-sectional view showing an optical arrangement of
a zoom optical system as Example 18.

[0041]FIG. 24 is a cross-sectional view showing an optical path diagram at
a wide angle end in the zoom optical system as Example 18.

[0060]FIG. 43 is a diagram showing moving directions of the lens groups in
the Examples of the zoom optical system embodying the invention.

[0061]FIG. 44 is a diagram showing moving directions of the lens groups in
the Examples of the zoom optical system embodying the invention.

[0062]FIG. 45 is a diagram showing moving directions of the lens groups in
the Examples of the zoom optical system embodying the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0063]In the following, an embodiment of the invention is described
referring to the drawings. The terms used in the following description
are defined as follows throughout the specification. [0064](a) The
refractive index is a refractive index with respect to a wavelength
(587.56 nm) of d-ray. [0065](b) The Abbe number is an Abbe number vd
which is obtained by the following definitional equation:

[0065]vd=(nd-1)/(nF-nC)

where nd, nF, and nC are refractive indexes with respect to d-ray, F-ray
(wavelength: 486.13 nm), and C-ray (wavelength: 656.28 nm), respectively,
and vd is the Abbe number. [0066](c) The indication concerning a plane
configuration is an indication based on paraxial curvature. [0067](d) The
optical power concerning each of single lens elements constituting a
cemented lens element is defined in a condition that both lens surfaces
of the individual single lens elements face the air. [0068](e) The amount
of aspherical sag is a parameter representing a difference between an
amount of spherical sag based on paraxial curvature, and an optical axis
distance from a vertex of a lens surface to a point on a curve of an
aspherical surface with respect to a maximum effective radius (see FIG.
2). [0069](f) A resin material to be used as a material for a composite
aspherical lens element (a lens element with an aspherical shape, which
is obtained by coating a film of resin material on a spherical glass
member as a substrate) merely has an additive function of a glass
substrate. Accordingly, the composite aspherical lens element is not
handled as an individual optical member, but is handled as a single lens
element based on a premise that the glass substrate has an aspherical
surface. In this case, the refractive index of the glass material
composing the glass substrate is defined as the refractive index of the
composite aspherical lens element. [0070](g) Concerning the lens
elements, the indication "concave", "convex", or "meniscus" shows a shape
of a lens element near the optical axis i.e. near the center of the lens
element, in other words, shows a shape based on paraxial curvature.

[0071]<Description on Arrangement of Zoom Optical System>

[0072]FIG. 1 is an optical path diagram at a wide angle end, showing an
arrangement example of a zoom optical system 100 embodying the invention.
The zoom optical system 100 is adapted to form an optical image of a
subject H on a light receiving surface of an image sensor 105 for
converting the optical image into an electric signal. The zoom optical
system 100 is a zoom optical system, wherein a first lens group 101
having a negative optical power, a second lens group 102 having a
positive optical power, and a third lens group 103 having a positive or
negative optical power are arranged in this order from an object side
i.e. the side of the subject H, and the interval between the first lens
group 101 and the second lens group 102 is decreased in zooming from a
wide angle end to a telephoto end.

[0073]In this embodiment, the first lens group 101 is constituted of a
biconcave negative lens element 1011, and a positive meniscus lens
element 1012 convex to the object side; the second lens group 102 is
constituted of a biconvex positive lens element 1021, and a negative
meniscus lens element 1022 convex to the object side; and the third lens
group 103 is constituted merely of a positive meniscus lens element 1031
convex to the object side. An optical diaphragm 104 is arranged on the
object side of the second lens group 102. The image sensor 105 is
arranged on the image side of the zoom optical system 100 by way of a
low-pass filter 106. In the zoom optical system 100 having the above
arrangement, an optical image of the subject H is guided along an optical
axis AX toward the light receiving surface of the image sensor 105 with a
proper zoom ratio, whereby the optical image of the subject H is captured
by the image sensor 105.

[0074]In the embodiment of the invention, the zoom optical system 100
having the above arrangement has a feature that the positive lens element
(in the example of FIG. 1, the positive meniscus lens element 1031) in
the third lens group 103 or in a lens group closer to the image side than
the third lens group 103 is made of a high dispersive material satisfying
a relation: vp<40 where vp is a minimum value of the Abbe number, as
shown in the aforementioned conditional expression (1). With this
arrangement, even if the optical power of the second lens group 102 is
increased to miniaturize the zoom optical system 100, magnification
chromatic aberration at the telephoto end can be sufficiently corrected.
Preferably, the minimum value vp of the Abbe number satisfies the
following conditional expression [0075](1)' to sufficiently correct the
magnification chromatic aberration even in use of an image sensor with a
high pixel resolution and an extremely small pixel pitch as the image
sensor 105:

[0075]vp<32 (1)'

Setting the minimum value vp of the Abbe number smaller than 32 enables to
perform an imaging operation with a sufficiently large contrast, without
likelihood that correction of magnification chromatic aberration may be
insufficient, even in use of the image sensor 105 with a high number of
pixels and an extremely small pixel pitch.

[0076]In the following, preferred arrangements on the first through the
third lens groups 101 through 103, arrangements of the other lens group
i.e. a fourth lens group, and preferred arrangements concerning the
entirety of the zoom optical system 100 are described one by one.

[0077](First Lens Group 101)

[0078]As shown in FIG. 1, preferably, the first lens group 101 is
constituted, in the order from the object side, the biconcave negative
lens element 1011 and the positive meniscus lens element 1012 convex to
the object side. Alternatively, a negative meniscus lens element convex
to the object side may be provided, in place of the biconcave negative
lens element 1011. With the lens arrangement as mentioned above, a back
focus distance at the wide angle end can be easily secured, and
astigmatism or magnification chromatic aberration of an off-axis ray at a
wide angle of view can be desirably corrected. Also, arranging the
positive meniscus lens element 1012 convex to the object side enables to
desirably correct astigmatism, thereby improving the quality of an image.

[0079]Preferably, the first lens group 101 includes a cemented lens
element (in the example of FIG. 1, the negative lens element 1011 and the
positive meniscus lens element 1012 are cemented to each other).
Including the cemented lens element in the first lens group 101 is
advantageous in remarkably reducing decentering error sensitivity of each
lens surface in the first lens group 101, and maintaining sensitivity
balance in an intended condition even in need of adjustment between lens
elements. Further, the lens barrel arrangement of the first lens group
101 can be simplified.

[0080]Preferably, the first lens group 101 satisfies the following
conditional expressions (10) and (11):

1.5|f1/fw|<3.5 (10)

0.5|f1/ft|<1.5 (11)

where f1: a composite focal length of the first lens group

[0081]fw: a composite focal length of the entirety of the optical system
at the wide angle end

[0082]ft: a composite focal length of the entirety of the optical system
at the telephoto end

[0083]If |f1/fw| and |f1/ft| are over the upper limits in the conditional
expressions (10) and (11), respectively, particularly, correction of
astigmatism or distortion aberration at the wide angle end is
insufficient. On the other hand, if |f1/fw| and |f1/ft| are under the
lower limits in the conditional expressions (10) and (11), respectively,
the power of each lens element constituting the first lens group 101 may
be unduly increased, which makes it difficult to produce an intended zoom
optical system. In addition, correction of magnification chromatic
aberration may be insufficient.

[0084]Preferably, the first lens group 101 satisfies the following
conditional expressions (10)' and (11)':

1.8|f1/fw|<3.0 (10)'

0.6|f1/ft|<1.2 (11)'

[0085]If |f1/fw| and |f1/ft| are over the upper limits in the conditional
expressions (10)' and (11)', respectively, the negative optical power of
the first lens group 101 is weakened, which may increase the diameter of
the forwardmost lens element. On the other hand, if |f1/fw| and |f1/ft|
are under the lower limits in the conditional expressions (10)' and
(11)', respectively, particularly, error sensitivity of the first lens
group 101 at the telephoto end is increased, which may require an
adjustment between lens elements.

[0086](Second Lens Group 102)

[0087]As shown in the following conditional expression (4), preferably,
the second lens group 102 satisfies the following relation:

0.7<f2/fw<2.0

where f2 is a composite focal length of the second lens group 102, and fw
is a composite focal length of the entirety of the optical system at the
wide angle end. With this arrangement, an intended zoom ratio can be
obtained, while securing miniaturization of the zoom optical system 100.
Particularly preferably, the second lens group 102 satisfies the
requirement represented by the following conditional expression (4)'.

0.8<f2/fw<1.8 (4)'

[0088]If f2/fw is over the upper limit in the conditional expression (4)',
the power of the second lens group 102 is weakened. As a result, the
moving amount of the second lens group 102 necessary for zooming is
increased, which may increase the entire length of the optical system. On
the other hand, if f2/fw is under the lower limit in the conditional
expression (4)', decentering error sensitivity of the second lens group
102 is increased, which may necessitate an adjustment between lens
elements, thereby increasing the production cost.

[0089]Preferably, the second lens group 102 satisfies the following
conditional expression (7), in the case where the second lens group 102
is constituted of a positive lens element and a negative lens element in
this order from the object side, as exemplified by the arrangement shown
in FIG. 1, in which the second lens group 102 is constituted of the
biconvex positive lens element 1021 and the negative meniscus lens
element 1022 convex to the object side:

0.7<|f2n/f2p|<1.8

where f2n is a focal length of the negative lens element in the second
lens group 102, and f2p is a focal length of the positive lens element in
the second lens group 102. Particularly preferably, the second lens group
102 satisfies the requirement represented by the following conditional
expression (7)':

0.9<|f2n/f2p|<1.5 (7)'

[0090]If |f2n/f2p| is over the upper limit or under the lower limit in the
conditional expression (7)', the powers of the negative lens element and
the positive lens element may be unduly increased in an attempt to
correct spherical aberration, axial chromatic aberration, or
magnification chromatic aberration. As a result, production error
sensitivity may be increased, thereby lowering productivity.

[0091]Preferably, the second lens group 102 satisfies the following
conditional expression (12):

0.3<f2/ft<0.9 (12)

[0092]If f2/ft is over the upper limit in the conditional expression (12),
the power of the second lens group 102 is weakened, which may make it
difficult to obtain a zoom ratio of about two to three times. On the
other hand, if f2/ft is under the lower limit in the conditional
expression (12), error sensitivity of the second lens group 102 is unduly
increased, which may make it difficult to produce an intended optical
system.

[0093]Particularly preferably, the second lens group 102 satisfies the
requirement represented by the following conditional expression (12)':

0.4<f2/ft<0.8 (12)'

[0094]If f2/ft is over the upper limit in the conditional expression
(12)', the power of the second lens group 102 is weakened. As a result,
the moving amount of the second lens group 102 required for zooming is
increased, thereby increasing the entire length of the optical system,
which may hinder miniaturization. On the other hand, if f2/ft is under
the lower limit in the conditional expression (12)', decentering error
sensitivity of the second lens group 102 is increased, which may
necessitate an adjustment between lens elements, thereby increasing the
production cost.

[0095]Preferably, the second lens group 102 includes a cemented lens
element (in the example of FIG. 1, the biconvex positive lens element
1021 and the negative meniscus lens element 1022 are cemented to each
other). Including the cemented lens element in the second lens group 102
is advantageous in remarkably reducing error sensitivity of each lens
surface in the second lens group 102, and simplifying the lens barrel
arrangement of the second lens group 102.

[0096]Further preferably, at least one surface of the positive lens
element in the second lens group 102 (in the example of FIG. 1, the
biconvex positive lens element 1021) has an aspherical shape. This
arrangement enables to desirably correct spherical aberration and coma
aberration resulting from increase of the power of the second lens group
102 by miniaturization.

[0097](Third Lens Group 103)

[0098]As shown in the following conditional expression (2), the positive
lens element satisfying the conditional expression (1), which is included
in the third lens group 103 or included in the lens group closer to the
image side than the third lens group 103, in other words, the positive
meniscus lens element 1031 shown in FIG. 1, uses a high refractive glass
material satisfying: Npg>1.7 where Npg is a refractive index of d-ray.
This arrangement enables to reduce a difference in incident angle with
respect to the image sensor 105 between the wide angle end and the
telephoto end, thereby making it easy to produce the zoom optical system.

[0099]The positive meniscus lens element 1031 can be made of a resin
material. In this case, it is desirable to use a resin material having a
refractive index satisfying the following conditional expression (3):
Npp>1.55 where Npp is a refractive index of d-ray with respect to the
positive lens element made of the resin material. This arrangement
enables to configure the zoom optical system 100 capable of sufficiently
correcting magnification chromatic aberration or the like.

[0100]The principal point position of the lens element can be set away
from the imaging plane by shaping the positive lens element satisfying
the conditional expression (1) into the positive meniscus lens element
1031 convex to the object side as shown in FIG. 1. Thereby, the incident
angle of the incident ray with respect to the imaging plane can be
reduced. Thus, this arrangement is advantageous in microminiaturizing the
zoom optical system 100.

[0101]As shown in the following conditional expression (8), preferably,
the positive meniscus lens element 1031 satisfies the following
requirement:

0.05<|ΔZpi/di|<0.25

where ΔZpi is an amount of aspherical sag, at a maximum effective
radius, of an image-side lens surface of the positive lens element having
the Abbe number satisfying the conditional expression(1), and di is the
maximum effective radius of the image-side lens surface of the positive
lens element having the Abbe number. This enables to optimize a plane
angle at a periphery of the lens element and suppress lowering of a
peripheral illuminance.

[0102]As shown in the following conditional expression (9), preferably,
the positive meniscus lens element 1031 satisfies the following
requirement: 1<fp/fw<8 where fp is a focal length of the positive
lens element having the Abbe number satisfying the conditional expression
(1) in the aspect of sufficiently correcting magnification chromatic
aberration. Particularly preferably, the positive meniscus lens element
1031 satisfies the requirement represented by the following conditional
expression (9)':

4<fp/fw<7 (9)'

[0103]If fp/fw is over the upper limit in the conditional expression (9)',
an aspherical surface is essentially required to bring an incident angle
of an incident ray with respect to the imaging plane closer to a
telecentric state. Also, the amount of aspherical sag may be increased,
thereby increasing the production cost. On the other hand, if fp/fw is
under the lower limit in the conditional expression (9)', a difference in
incident angle with respect to the imaging plane between the wide angle
end and the telephoto end may be increased, which may lower a peripheral
illuminance.

[0104]In this section, the amount of aspherical sag defined in the above
is described referring to FIG. 2. Now, let it be assumed that the optical
axis direction corresponds to a horizontal axis, the lens radial
direction corresponds to a vertical axis, and an intersection between the
horizontal axis and the vertical axis corresponds to a vertex "a" on a
lens surface. Also, let it be assumed that p1 represents a curve of a
spherical surface, p2 represents a curve of an aspherical surface, and
"r" represents a maximum effective radius of a lens element constituted
of the spherical surface and the aspherical surface. Then, the amount of
spherical sag (sag/sagitta) corresponds to an optical axis distance
between the vertex "a" of the lens surface, and a point on the curve p1
of the spherical surface with respect to the maximum effective radius
"r". The amount of aspherical sag is a parameter representing a
difference between the amount of spherical sag, and an optical axis
distance from the vertex "a" of the lens surface to a point on the curve
p2 of the aspherical surface with respect to the maximum effective radius
"r".

[0106]If fp/ft is over the upper limit in the conditional expression (13),
correction of magnification chromatic aberration may be insufficient. On
the other hand, if fp/ft is under the lower limit in the conditional
expression (13), correction of magnification chromatic aberration may be
excessive. In both of the cases, image quality in a peripheral portion of
the lens element may be degraded.

[0107]The positive meniscus lens element 1031 may have at least one
aspherical surface. Providing the aspherical surface allows for
sufficient correction of astigmatism/distortion aberration, despite a
slight disadvantage in terms of production cost. Further, latitude in
adjusting the incident angle of an optical image with respect to the
image sensor 105 can be increased, and a difference in incident angle
with respect to the image sensor 105 between the wide angle end and the
telephoto end can be reduced, which enables to obtain an image with less
likelihood that a peripheral portion may have an unduly small light
amount.

[0108](Various Preferred Arrangements on Zoom Optical System) As shown in
the following conditional expressions (5) and (6), preferably, the zoom
optical system 100 satisfies the following relation:

0<αw<30

|αw-αt|<20

where αw is an angle (deg) of a principal ray, at a maximum image
height, of incident rays onto an imaging surface of the image sensor 105
with respect to a normal to the imaging plane at the wide angle end; and
at is an angle (deg) of a principal ray, at the maximum image height, of
the incident rays onto the imaging surface with respect to the normal to
the imaging plane at the telephoto end. The angles αw (deg),
αt (deg) are defined based on a premise that the direction shown in
FIG. 3 is a plus direction. Specifically, assuming that the left side in
FIG. 3 is an object side, and the right side in FIG. 3 is an image side,
it is defined that the angle of a principal ray in the case where the
exit pupil position is on the object side with respect to the imaging
plane is in the plus direction.

[0109]Particularly preferably, the zoom optical system 100 satisfies the
requirement represented by the following conditional expression (5)':

10<αw<25 (5)'

[0110]If αw is over the upper limit in the conditional expression
(5)', use of a high-pixel image sensor is difficult to maintain the
peripheral illuminance in an intended condition. This is because in use
of image sensors of the same size, as the pixel number is increased, the
pixel pitch is reduced, and the aperture efficiency is lowered, which
makes it difficult to secure adequate telecentricity. On the other hand,
if αw is under the lower limit in the conditional expression (5)',
it is difficult to secure miniaturization.

[0111]Particularly preferably, the zoom optical system 100 satisfies the
requirement represented by the following conditional expression (6)':

|αw-αt|<15

[0112]If |αw-αt| is over the upper limit in the conditional
expression (6)', use of a high-pixel image sensor is difficult to
maintain peripheral illuminance both at the wide angle end and the
telephoto end in an intended condition. This is because in use of image
sensors of the same size, as the pixel number is increased, the pixel
pitch is reduced, and the aperture efficiency is lowered, which makes it
difficult to secure adequate telecentricity.

[0113]Preferably, the zoom optical system 100 satisfies the following
conditional expression (14).

0.1<Y'/TL<0.3 (14)

where Y': a maximum image height

[0114]TL: a maximum value of an optical axis distance from a vertex on a
lens surface closest to the object side to the imaging plane in the
entire zoom range

[0115]If Y'/TL is over the upper limit in the conditional expression (14),
the power of the second lens group 102 is unduly increased, because the
moving amount of the second lens group 102 for zooming is decreased. As a
result, it is difficult to satisfy the production requirements such as
radius of curvature of each lens element constituting the second lens
group 102. On the other hand, if Y'/TL is under the lower limit in the
conditional expression (14), it is difficult to mount the zoom optical
system in a mobile phone or a like device, considering the size
constraints.

[0116]Particularly preferably, the zoom optical system 100 satisfies the
following conditional expression (14)':

0.13<Y'/TL<0.2 (14)'

[0117]If Y'/TL is over the upper limit in the conditional expression
(14)', the power of the second lens group 102 is unduly increased, which
may increase error sensitivity in the second lens group 102. As a result,
adjustment between lens elements is required, which may increase the
production cost. On the other hand, if Y'/TL is under the lower limit in
the conditional expression (14)', not only the size of the optical system
but also a load of a driving member resulting from an increase in moving
amount in zooming is increased. As a result, the size of the driving
device may be increased.

[0118]Preferably, the zoom optical system 100 satisfies the following
conditional expression (15):

0.2<t2/TL<0.4 (15)

where t2 is a distance required for the second lens group to move in
zooming from the wide angle end to the telephoto end.

[0119]If t2/TL is over the upper limit in the conditional expression (15),
it is difficult to secure a space for installing a mechanical shutter
which is effective in preventing smear. Also, the lens barrel arrangement
may be complicated in order to avoid contact among driving members, which
may resultantly increase the production cost. On the other hand, if t2/TL
is under the lower limit in the conditional expression (15), decentering
error sensitivity of the second lens group 102 is increased, which may
make it difficult to produce an intended zoom optical system.

[0120]Preferably, the zoom optical system 100 satisfies the following
conditional expression (16):

Lb/fW<2 (16)

where Lb is an optical axis distance (length in terms of air) from a
vertex on a lens surface which is closest to the image sensor and which
has an optical power to the surface of the image sensor at the telephoto
end.

[0121]If Lb/fW is over the upper limit in the conditional expression (16),
it is required to increase the negative optical power of the first lens
group 101 to secure a long back focus distance, which may increase the
curvature of the negative lens element in the first lens group 101 and
make it difficult to produce an intended zoom optical system.

[0122]One of the most preferred lens arrangements in the embodiment of the
invention is, as shown in FIG. 1, the zoom optical system 100 constituted
merely of the first through the third lens groups 101 through 103,
wherein the third lens group 103 is constituted of a single positive lens
element i.e. the positive meniscus lens element 1031. Thus, the zoom
optical system 100 can be miniaturized, as compared with the other zoom
optical system, by minimizing the number of lens groups or the number of
lens elements. In the three-component zoom optical system of
negative-positive-positive arrangement, the third lens group 103 can be
relatively easily constituted of a single lens element, because the third
lens group 103 has a smaller optical power than the first lens group 101
or the second lens group 102. If the above lens arrangement is adopted,
it is desirable to fix the third lens group 103 in zooming from the wide
angle end to the telephoto end. The lens barrel mechanism can be
simplified, and the position precision of the lens elements can be
improved by fixing the third lens group 103 in zooming.

[0123]Preferably, in the zoom optical system 100, the first lens group 101
and the second lens group 102 each is constituted of three or less lens
elements. With this arrangement, it is possible to reduce the load of the
driving device for driving the first lens group 101 whose outer diameter
is generally inherently large, and for driving the second lens group
whose moving amount in zooming is large. This enables to reduce the
production cost by decreasing the number of lens elements. The zoom
optical system 100 shown in FIG. 1 has a preferred lens arrangement for
this reason as well as the aforementioned reasons.

[0124]As shown in the zoom optical system 100 of FIG. 1, it is desirable
to arrange the optical diaphragm 104 i.e. an aperture stop on the object
side of the second lens group 102, and to fix the aperture diameter of
the optical diaphragm 104. First, the diameter of the forwardmost lens
element in the first lens group 101 can be maximally reduced by arranging
the optical diaphragm 104 on the object side of the second lens group
102. Further, there is no need of increasing the interval between the
first lens group 101 and the second lens group 102 beyond a required
amount by fixing the aperture diameter, which enables to reduce the
thickness of the zoom optical system 100 in the optical axis direction.

[0125]Next, concerning the focusing arrangement of the zoom optical system
100, it is desirable to allow focusing from an infinite object distance
to a close object distance by moving the first lens group 101 to the
object side. This is because the above arrangement enables to suppress
performance degradation by focusing, considering an advantage that the
change in various aberrations resulting from moving the first lens group
101 is relatively small. Also, since large back focus change relative to
the moving amount of the first lens group 101 is secured, it is possible
to obtain desirable focusing performance up to a position close to the
lens element by about several centimeters with a less moving amount.

[0126]Preferably, focusing from an infinite object distance to a close
object distance is performed by moving the third lens group 103 to the
object side. This arrangement enables to obtain a clear image up to the
close object distance without likelihood that the entire length of the
optical system by protrusion of a lens barrel, or the diameter of the
forwardmost lens element may be unduly increased. Judgment as to whether
the first lens group 101 or the third lens group 103 is to be moved in
focusing is determined depending on the optical specifications of the
zoom optical system 100. Specifically, the first lens group 101 is moved
in activating the macro function, and the third lens group 103 is moved
in prioritizing miniaturization of the zoom optical system 100.

[0127](Arrangement having Fourth Lens Group)

[0128]Preferably, the zoom optical system 100 has one or more lens groups
closer to the image side than the third lens group 103. For instance, the
zoom optical system 100 may have a fourth lens group (not shown in FIG.
1) which has one or more lens elements and which is arranged between the
third lens group 103 and the low-pass filter 106.

[0129]For instance, the zoom optical system is configured into a
four-component zoom optical system 100 of
negative-positive-negative-positive arrangement, wherein the third lens
group 103 has a negative optical power, and the fourth lens group has a
positive optical power. In this arrangement, axial chromatic aberration
can be sufficiently corrected by the third lens group 103 having a
negative optical power. This enables to enhance the contrast at the
center of a captured image on a display screen. Also, intended optical
performance with respect to a close object can be easily secured by
providing the fourth lens group.

[0130]In the four-component zoom optical system 100 of
negative-positive-negative-positive arrangement, it is desirable to
provide a positive lens element having the Abbe number satisfying the
conditional expression (1) in the fourth lens group. The fourth lens
group closer to the image side is located at such a position that the
principal ray height of an off-axis ray is set high. Using the positive
lens element having the Abbe number as the positive lens element in the
fourth lens group is advantageous in correcting magnification chromatic
aberration. In this case, preferably, the fourth lens group is
constituted of a positive lens element. In the four-component zoom
optical system, since the fourth lens group has a smaller optical power
than the first lens group 101 or the second lens group 102, it is
relatively easy to constitute the fourth lens group of a single lens
element. This is further advantageous in miniaturizing the zoom optical
system 100.

[0131]Preferably, in the four-component zoom optical system 100 of
negative-positive-negative-positive arrangement, the fourth lens group is
fixed in zooming from the wide angle end to the telephoto end. The lens
barrel mechanism can be simplified, and the position precision of the
lens elements can be improved by fixing the fourth lens group in zooming.
Preferably, the first lens group 101 is fixed in zooming from the wide
angle end to the telephoto end. The first lens group 101 whose outer
diameter is inherently large greatly affects the dimensions of the zoom
optical system 100. Therefore, fixing the first lens group 100 in zooming
is advantageous in simplifying the lens barrel mechanism, which is
advantageously effective in miniaturizing the zoom optical system 100 in
length, width, and thickness directions.

[0132]In the four-component zoom optical system 100 of
negative-positive-negative-positive arrangement, it is particularly
desirable to fix both of the first lens group 101 and the fourth lens
group 104 in zooming from the wide angle end to the telephoto end. With
this arrangement, the weight of the lens groups to be driven in zooming
with use of the four-component zoom optical system 100 can be maximally
reduced. This allows for use of a small-sized driving device as a zoom
mechanism, which is further advantageous in miniaturizing the zoom
optical system as a lens unit.

[0133]The zoom optical system 100 provided with the fourth lens group can
be configured into a four-component zoom optical system 100 of
negative-positive-positive-negative arrangement, wherein the third lens
group 103 has a positive optical power, and the fourth lens group has a
negative optical power. In this arrangement, the incident angle of the
incident ray with respect to the light receiving surface of the image
sensor 105 disposed on the imaging plane is allowed to have adequate
telecentricity by providing the third lens group 103 having a positive
optical power. Also, intended optical performance with respect to a close
object can be easily secured by providing the fourth lens group.

[0134]Preferably, in the four-component zoom optical system 100 of
negative-positive-positive-negative arrangement, a positive lens element
having the Abbe number satisfying the aforementioned conditional
expression (1) is provided in the third lens group 103. The third lens
group 103 relatively close to the image side is located at such a
position that the principal ray height of an off-axis ray is set high.
Using the positive lens element having the Abbe number as the positive
lens element in the third lens group 103 is advantageous in correcting
magnification chromatic aberration. In this case, preferably, the third
lens group 103 is constituted of a single positive lens element. In the
four-component zoom optical system 100, since the third lens group 103
has a smaller optical power than the first lens group 101 or the second
lens group 102, it is relatively easy to constitute the third lens group
103 of a single lens element. This is further advantageous in
miniaturizing the zoom optical system 100.

[0135]Similarly to the reason as described in the example concerning the
negative-positive-negative-positive arrangement, in the four-component
zoom optical system 100 of negative-positive-positive-negative
arrangement, preferably, the fourth lens group, or the first lens group
101, or both of the fourth lens group and the first lens group 101 is
fixed in zooming from the wide angle end to the telephoto end.

[0136](Other Arrangement on Zoom Optical System)

[0137]Concerning a process for manufacturing the zoom optical system 100,
there is no specific constraint on the material of each lens element
constituting the first through the third lens group 101 through 103 (and
the fourth lens group). Various glass materials or resin (plastic)
materials may be used, as far as the optical material satisfies the
requirements concerning the minimum value vp of the Abbe number. Use of a
resin material, however, is advantageous in suppressing the production
cost or reducing the weight of the zoom optical system 100, because the
resin material is lightweight, and mass production of the resin material
is feasible by injection molding or a like process.

[0138]In the case where at least two lens elements made of a resin
material are used, it is desirable to form the negative lens element in
the first lens group 101 i.e. the negative lens element 1011 in FIG. 1,
and the positive lens element satisfying the conditional expression (1)
i.e. the positive meniscus lens element 1031 of the resin material. This
arrangement enables to suppress back focus error accompanied by ambient
temperature change.

[0139]In the case where an aspherical glass lens element is used in the
zoom optical system 100, the aspherical glass lens element may be
produced by molding, or by combining a glass material and a resin
material. The molded lens element can be mass-produced, but the kind of
glass material to be used in the molded lens element is limited. The
composite glass/resin lens element has advantages that there are many
kinds of glass material to be used as a substrate, and design latitude is
high. Generally, it is difficult to produce an aspherical lens element
using a high refractive material by molding. Accordingly, the advantages
of the composite lens element can be maximally utilized by producing a
lens element having a single aspherical surface.

[0140]Preferably, in the zoom optical system 100, all the lens surfaces
facing the air are aspherical. This arrangement enables to miniaturize
the zoom optical system 100 while attaining high-quality performance.

[0141]Preferably, the zoom optical system 100 has a mechanical shutter
having a function of blocking light from the image sensor 105, in place
of the optical diaphragm 104. The mechanical shutter is effective in
preventing smear in the case where a CCD (Charge Coupled Device) sensor
is used as the image sensor, for instance.

[0142]A conventional well-known cam mechanism or stepping motor may be
used as a drive source for driving the lens groups, the diaphragm, the
shutter, or a like member provided in the zoom optical system 100. In the
case where the moving amount is small, or the weight of the driving
members is light, use of a microminiaturized piezoelectric actuator
enables to drive the driving members independently of each other, while
suppressing increase in volume of the driving device or electric power
consumption, which is further advantageous in miniaturizing an imaging
lens device incorporated with the zoom optical system 100.

[0143]One of the most preferred lens arrangements in the embodiment of the
invention is the zoom optical system 100, as shown in FIG. 1, which is
constituted of the first lens group 101, the second lens group 102, and
the third lens group 103 in this order from the object side, wherein the
first lens group 101 is constituted of the negative lens element i.e. the
negative lens element 1011, and the positive meniscus lens element convex
to the object side i.e. the positive meniscus lens element 1012, the
second lens group 102 is constituted of the biconvex lens element i.e.
the biconvex positive lens element 1021, and the negative lens element
i.e. the negative meniscus lens element 1022, and the third lens group
103 is constituted of the positive lens element i.e. the positive
meniscus lens element 1031. Specifically, the principal point position of
the second lens group 102 can be approximated to the first lens group 101
by arranging the positive lens element and the negative lens element in
the second lens group 102 in this order from the object side. This
enables to reduce the substantial power of the second lens group 102
while keeping the zoom function, thereby enabling to reduce error
sensitivity. Also, the power of the second lens group 102 can be
increased by arranging the biconvex lens element in the second lens group
102. This enables to reduce the moving amount of the second lens group
102 in zooming. Further, constituting the third lens group 103 of the
positive lens element is advantageous in approximating the incident angle
of an off-axis ray onto the light receiving surface of the image sensor
105 to a telecentric state.

[0144]The image sensor 105 is adapted to photoelectrically convert an
optical image of a subject H formed by the zoom optical system 100 into
image signals of color components of R, G, and B in accordance with the
light amount of the subject image for outputting the image signals to a
predetermined image processing circuit. For instance, the image sensor
105 is a one-chip color area sensor of a so-called "Bayer matrix", in
which patches of color filters each in red (R), green (G), and blue (B)
are attached in a checkered pattern on respective surfaces of CCDs
arrayed in two dimensions. Examples of the image sensor 105 are a CMOS
image sensor, and a VMIS image sensor in addition to the CCD image
sensor.

[0145]The low-pass filter 106 is a parallel-plane optical component which
is disposed on the imaging surface of the image sensor 105 for removing
noise components. Examples of the low-pass filter 106 are e.g. a
birefringent low-pass filter made of a crystal or a like material, whose
predetermined crystalline axis direction is regulated, and a phase
low-pass filter for realizing required optical cutoff frequency
characteristic by a diffraction effect. It is not necessarily required to
provide the low-pass filter 106. Further alternatively, an infrared
cutoff filter may be used to reduce noise included in an image signal
from the image sensor 105, in place of the aforementioned optical
low-pass filter 106. Further alternatively, the function of the
birefringent low-pass filter and the function of the phase low-pass
filter may be realized by a single low-pass filter by applying infrared
reflective coat to a surface of the optical low-pass filter 106.

[0147]In this section, a digital apparatus incorporated with the
aforementioned zoom optical system 100 is described. FIGS. 4A and 4B are
diagrams showing an external appearance of a camera phone 200, as an
example of a digital apparatus embodying the invention. In this
embodiment, the digital apparatus includes a digital still camera, a
video camera, a digital video unit, a PDA (Personal Digital Assistant), a
personal computer, a mobile computer, and peripheral devices thereof such
as a mouse, a scanner, and a printer. A digital still camera and a
digital video camera are an imaging lens device configured in such a
manner that, after an image of a subject is optically read, the subject
light image is converted into an electric signal, using a semiconductor
device i.e. an image sensor, for storing the electric signal as digital
data into a storage medium such as a flash memory. The embodiment of the
invention also includes a mobile phone, a personal digital assistant, a
personal computer, a mobile computer, and peripheral devices thereof,
which are incorporated with a compact imaging lens device for optically
reading a still image or a moving image of a subject.

[0148]FIG. 4A is a diagram showing an operating surface of the mobile
phone 200, and FIG. 4B is a diagram showing a back surface of the mobile
phone 200. The mobile phone 200 has an antenna 201 at an upper part
thereof, and, on the operating surface thereof, a substantially
rectangular display 202, an image changeover button 203 for activating
the image photographing mode, and changing over the image photographing
mode between still image shooting and moving image shooting, a zoom
button 204 for controlling zooming, a shutter button 205, and a dial
button 206. The symbol "T" representing zooming to the telephoto end and
the symbol "W" representing zooming to the wide angle end are marked on
an upper part and a lower part of the zoom button 204, respectively. The
zoom button 204 includes a two-contact switch which is operated in such a
manner that a designated zoom is performed when the relevant marked part
is depressed. The mobile phone 200 is built-in with the imaging lens
device 207 incorporated with the aforementioned zoom optical system 100.

[0149]FIG. 5 is a functional block diagram showing an electric
configuration relating to an imaging operation to be executed by the
mobile phone 200. The mobile phone 200 includes an imaging section 10, an
image generator 11, an image data buffer 12, an image processor 13, a
driver 14, a controller 15, a storage 16, and an I/F 17 for imaging
functions.

[0150]The imaging section 10 includes the imaging lens device 207 and the
image sensor 105. The imaging lens device 207 has the zoom optical system
100 with the arrangement as shown in FIG. 1, and an unillustrated lens
driving device for driving the lens elements in the optical axis
direction for zooming and focusing. Light rays from a subject are formed
on the light receiving surface of the image sensor 105 by the zoom
optical system 100, whereby an optical image of the subject is obtained.

[0151]The image sensor 105 converts the optical image of the subject
formed by the zoom optical system 100 into electric signals of color
components of R (red), G (green), and B (blue) for outputting to the
image generator 11 as image signals of the colors of R, G, and B. The
image sensor 105 is operative to perform an imaging operation such as one
of still image sensing operation and moving image sensing operation, or a
readout operation (horizontal scanning, vertical scanning, transfer) of
an output signal from each pixel in the image sensor 105 under the
control of the controller 15.

[0152]The image sensor 11 performs amplification processing, digital
conversion processing, or a like processing with respect to an analog
output signal from the image sensor 105; and performs well-known image
processing such as determination of proper black level with respect to
the entirety of the image, gamma correction, white balance (WB)
adjustment, contour correction, or color disparity correction to generate
image data of each pixel from the image signal. The image data generated
by the image generator 11 is outputted to the image data buffer 12.

[0153]The image data buffer 12 temporarily stores the image data, and is a
memory to be used as a work area for allowing the image processor 13 to
perform a below-mentioned processing with respect to the image data. The
image data buffer 12 is e.g. constituted of an RAM (Random Access
Memory).

[0154]The image processor 13 is a circuit for performing image processing
such as resolution conversion with respect to the image data temporarily
stored in the image data buffer 12. The image processor 13 may be so
configured as to correct aberration that has not been corrected by the
zoom optical system 100, according to needs. The driver 14 drives the
lens groups of the zoom optical system 100 in such a manner that intended
zooming and focusing are performed based on a control signal outputted
from the controller 15.

[0155]The controller 15 includes e.g. a microprocessor, and controls
respective operations of the imaging section 10, the image generator 11,
the image data buffer 12, the image processor 13, the driver 14, the
storage 16, and the I/F 17. Specifically, the controller 15 controls the
imaging lens device 207 and the image sensor 105 to perform at least one
of still image shooting and moving image shooting for a subject.

[0156]The storage 16 is a storing circuit for storing the image data
generated by the still image shooting or the moving image shooting for
the subject. The storage 16 includes e.g. an ROM (Read Only Memory) or an
RAM. In other words, the storage 16 has a function as a memory for still
image or moving image. The I/F 17 is an interface for transmitting and
receiving image data to and from an external device. The I/F 17 is an
interface in conformity with the standards e.g. USB or IEEE1394.

[0157]An imaging operation to be executed by the mobile phone 200 having
the above arrangement is described. First, in shooting a still image, the
image photographing mode is activated by depressing the image changeover
button 203. In this embodiment, depressing the image changeover button
203 one time activates the still image shooting mode, and depressing the
image changeover button 203 once more in this state changes over the
image photographing mode to the moving image shooting mode. In other
words, in response to receiving a command from the image changeover
button 203, the controller 15 in the main body of the mobile phone 200
causes the imaging lens device 207 and the image sensor 105 to perform at
least one of still image shooting and moving image shooting for a subject
located on the object side.

[0158]When the still image shooting mode is activated, the controller 15
controls the imaging lens device 207 and the image sensor 105 to perform
still image shooting, and also drives the unillustrated lens driving
device in the imaging lens device 207 for focusing. Thereby, an optical
image of the subject in a focus state is cyclically formed on the light
receiving surface of the image sensor 105 for conversion into image
signals of color components of R, G, and B. Thereafter, the image signals
are outputted to the image generator 11. The image signals are
temporarily stored in the image data buffer 12 for image processing in
the image processor 13. After the image processing, the processed image
data is transferred to a memory (not shown) for the display 202 so that
an image is displayed on the display 202. The photographer is allowed to
view the display 202 and adjust the position of the displayed image in
such a manner that the main subject image is located in an intended
position within the display screen. When the photographer depresses the
shutter button 205 in this state, a still image can be acquired. In other
words, image data is stored in the storage 16 as a memory for still
image.

[0159]In the above operation, if the subject is located away from the
photographer, or the photographer wishes to obtain an enlarged image of
the subject nearby, and accordingly, zoom shooting is carried out, the
photographer depresses the upper part of the zoom button 204 where the
symbol "T" is marked. Then, the controller 15 is operative to drive the
lens groups for zooming in accordance with a depressed time, thereby
causing the zoom optical system 100 to continuously zoom the image. If
the photographer wishes to reduce the magnification of the subject image
because of excessive zooming or a like condition, the photographer
depresses the lower part of the zoom button 204 where the symbol "W" is
marked. Then, the controller 15 controls the zoom optical system 100 to
continuously zoom the image in accordance with a depressed time. In this
way, the photographer is allowed to adjust the magnification by using the
zoom button 204, even if the subject is away from the photographer.
Similarly to normal photographing with the same magnification, an
enlarged still image can be obtained by adjusting the position of the
displayed image in such a manner that the main subject image is located
in an intended position within the display screen, and by depressing the
shutter button 205 in this state.

[0160]In performing moving image shooting, after the still image shooting
mode is activated by depressing the image changeover button 203 one time,
the image photographing mode is changed over to the moving image shooting
mode by depressing the image changeover button 203 once again in this
state. Thereby, the controller 15 controls the imaging lens device 207
and the image sensor 105 to perform moving image shooting. Thereafter,
similarly to the operation to be executed in the still image shooting
mode, the photographer is allowed to view the display 202 and adjust the
position of the displayed image in such a manner that the subject image
obtained through the imaging lens device 207 is located in an intended
position within the display screen. Similarly to the operation to be
executed in the still image shooting mode, the photographer is allowed to
adjust the magnification of the subject image by using the zoom button
204. The moving image shooting is started in response to depressing the
shutter button 205 in this state. During the moving image shooting, the
photographer is allowed to desirably change the magnification of the
subject image by manipulating the zoom button 204.

[0161]In performing the moving image shooting, the controller 15 controls
the imaging lens device 207 and the image sensor 105 to perform moving
image shooting, and is operative to drive the unillustrated lens driving
device in the imaging lens device 207 for focusing. Thereby, an optical
image in a focus state is cyclically formed on the light receiving
surface of the image sensor 105 such as a CCD sensor for conversion into
image signals of color components of R, G, and B. Thereafter, the image
signals are outputted to the image generator 11. The image signals are
temporarily stored in the image data buffer 12 for image processing in
the image processor 13. Thereafter, the processed image data is
transferred to the memory for the display 202 so that an image is
displayed on the display 202. The moving image shooting is ended by
depressing the shutter button 205 again in this state. The acquired
moving image is sent to the storage 16 as a memory for moving image for
storing the moving image data.

[0162]<Description on Examples of Zoom Optical System>

[0163]In the following, examples of the zoom optical system 100 as shown
in FIG. 1, specifically, the zoom optical system 100 incorporated with
the imaging lens device 207 to be mounted in the camera phone 200, as
shown in FIGS. 4A and 4B, is described referring to the drawings.

Example 1

[0164]FIG. 6 is a cross-sectional view i.e. an optical path diagram, taken
along the optical axis (AX), showing an arrangement of lens groups in a
zoom optical system 100A as Example 1. The optical path diagrams in FIG.
6, and FIGS. 7 through 24 to be described later each shows a lens
arrangement at the wide angle end (W). Throughout Example 1, and Examples
2 through 18 to be described later, the lens groups include, in this
order from the object side in the drawings i.e. the left side in FIG. 6,
a first lens group (Gr1) having a negative optical power as a whole, a
second lens group (Gr2) having a positive optical power as a whole, and a
third lens group (Gr3) having a positive or negative optical power as a
whole. In other words, the lens arrangement is a negative dominant
arrangement, in which the first lens group closest to the object side has
a negative optical power.

[0165]The zoom optical system 100A in Example 1 shown in FIG. 6 has the
following lens group arrangement in the order from the object side.
Specifically, the first lens group (Gr1) has a negative optical power as
a whole, and is constituted of a biconcave negative lens element (L1) and
a positive meniscus lens element (L2) convex to the object side. The
second lens group (Gr2) has a positive optical power as a whole, and is
constituted of a biconvex positive lens element (L3) and a negative
meniscus lens element (L4) convex to the object side. An aperture stop
(ST) which is moved with the first lens group (Gr1) and the second lens
group (Gr2) in zooming is provided on the object side of the second lens
group (Gr2). The third lens group (Gr3) is constituted of a positive
meniscus lens element (L5) which has a positive optical power and is
convex to the object side. A light receiving surface of an image sensor
(SR) is arranged on the image side of the third lens group (Gr3) via a
plane parallel plate (FT). The plane parallel plate (FT) corresponds to
an optical low-pass filter, an infrared cutoff filter, a cover glass for
image sensor, or a like element.

[0166]Alternatively, a mechanical shutter may be provided in place of the
aperture stop (ST). In FIG. 6, a continuously zoomable zoom optical
system is described. Alternatively, a two-focal-point switching type zoom
optical system having the same optical arrangements in two optical units
may be employed to attain further miniaturization. In particular, in the
case where the first lens group (Gr1) makes a U-turn (or the trajectory
of the first lens group (Gr1) is convex toward the image side) in zooming
from the wide angle end to the telephoto end, and as a result, the entire
length of the optical system is substantially the same at the wide angle
end and the telephoto end, use of the two-focal-point switching type zoom
optical system is advantageous in miniaturizing the dimensions of the
zoom optical system including a driving mechanism as a lens unit, because
the first lens group (Gr1) can be fixed in zooming. These features are
also applied to Examples 2 through 18 to be described later (and
accordingly, repeated description thereof will be omitted in the
following).

[0167]In FIG. 6, the surface denoted by the symbol ri (i=1, 2, 3, . . . )
indicates the i-th lens surface from the object side (a cemented surface
constituting a cemented lens element is counted as a lens surface), and
the surface ri attached with an asterisk (*) is an aspherical surface.
The aperture stop (ST), both surfaces of the plane parallel plate (FT),
and the light receiving surface of the image sensor (SR) are each
regarded as one lens surface. The same definition is also applied to the
optical path diagrams (see FIGS. 7 through 24) concerning other Examples
to be described later, and the symbols in FIGS. 7 through 24 identical to
those in FIG. 6 have basically the same meaning as in FIG. 6. It should
be noted, however, that all the symbols have the same meaning. For
instance, although the same symbol (r1) is attached to the lens surface
closest to the object side throughout the drawings of FIGS. 6 through 24,
this does not mean that the curvatures or a like feature of the lens
surfaces attached with the symbol (r1) are identical throughout Examples.

[0168]In the above arrangement, an incident ray from the object side is
transmitted through the first lens group (Gr1), the second lens group
(Gr2), the third lens group (Gr3), and the parallel plane plate (FT) in
this order along the optical axis AX, and forms an optical image of the
object onto the light receiving surface of the image sensor (SR). Then,
the image sensor (SR) converts the optical image corrected by the
parallel plane plate (FT) into an electric signal. The electric signal is
subjected to a predetermined processing such as digital image processing
or image compression processing, according to needs. Thereafter, the
processed signal is recorded in a memory of a mobile phone, a personal
digital assistant, or a like device, as a digital video signal, or
transmitted to other digital apparatus wiredly or wirelessly.

[0169]FIG. 43 (and FIG. 44 and FIG. 45) is a diagram showing moving
directions of the lens groups in zooming. In FIG. 43 (and FIG. 44 and
FIG. 45), the moving directions of lens groups in Example 2 and
thereafter to be described later are also shown, as well as the moving
directions of the lens groups in Example 1. Similarly to the foregoing
embodiment, in FIG. 43 (and FIG. 44 and FIG. 45), the left side
corresponds to the object side, and the first lens group (Gr1), the
second lens group (Gr2), the third lens group (Gr3), and the fourth lens
group (Gr4) are arranged in this order from the object side. In FIG. 43
(and FIG. 44 and FIG. 45), the symbol "W" represents the wide angle end
where the focal length is the shortest, i.e., the angle of view is the
largest, and the symbol "T" represents the telephoto end where the focal
length is the longest, and the angle of view is the smallest. The symbol
"M" represents the middle (hereinafter, called as "mid point") between
the wide angle end (W) and the telephoto end (T). Although the actual
lens groups are moved linearly along the optical axis, in FIG. 43 (and
FIG. 44 and FIG. 45), the positions of the lens groups at the wide angle
end (W), the mid point (M), and the telephoto end (T) are shown in the
upper row, the middle row, and the lower row, respectively, in each of
the illustrations.

[0170]As shown in FIG. 43, in Example 1, the first lens group (Gr1) and
the second lens group (Gr2) are movable in zooming, and the third lens
group (Gr3) is fixed in zooming. Specifically, in zooming from the wide
angle end (W) to the telephoto end (T), the second lens group (Gr2) is
linearly moved toward the object side, and the first lens group (Gr1) is
moved in such a manner that the trajectory thereof is convex toward the
image side. It should be noted, however, in Example 1 and below-mentioned
Examples, the moving directions, the moving amounts, or the like of the
lens groups are varied depending on the optical powers of the lens
groups, the lens arrangement, or a like condition. For instance, in FIG.
43, although the second lens group (Gr2) is linearly moved, the movement
includes a case where the trajectory of the second lens group (Gr2) is
convex toward the object side or the image side, and a case where the
second lens group (Gr2) makes a U-turn.

[0171]Construction data concerning the lens elements in the zoom optical
system 100A in Example 1 are shown in Tables 1 and 2. Also, the values of
the conditional expressions (1) through (16) in the case where the
conditional expressions (1) through (16) are applied to the optical
system in Example 1 are shown in Table 37 to be described later.

[0172]Table 1 indicates, from the left-side column thereof, the lens
surface numbers, radii of curvature (unit: mm) of the respective lens
surfaces, distances i.e. axial surface distances (unit: mm) between the
lens surfaces in the optical axis direction at the wide angle end (W),
the mid point (M), and the telephoto end (T) in an infinite focal state,
refractive indices of the respective lens elements, and the Abbe numbers
of the respective lens elements. The value in each blank column regarding
the axial surface distance at the mid point (M) and the telephoto end (T)
is the same as that in the corresponding left-side column at the wide
angle end (W). The axial surface distances are distances calculated on
the presumption that the medium residing in the region between a pair of
opposing planes including an optical plane and an imaging plane is the
air. As shown in FIG. 6, the surface denoted by the symbol ri (i=1, 2, 3,
. . . ) indicates the i-th lens surface from the object side on the
optical path, and the surface ri attached with an asterisk (*) is an
aspherical surface, namely, a refractive optical plane of an aspherical
configuration or a plane having a refractive power substantially
equivalent to the action of an aspherical plane. Since the aperture stop
(ST), both surfaces of the plane parallel plate (FT), and the light
receiving surface of the image sensor (SR) are flat, respective radii of
curvature thereof are infinite (∞).

[0173]The aspherical configuration of the optical plane is defined by the
following conditional expression, wherein a vertex on the lens surface is
represented as the point of origin, and a local orthogonal coordinate
system (x, y, z) is used, with the direction from the object toward the
image sensor being the plus direction of the z-axis.

[0179]As is obvious from the conditional expression (17), the radii of
curvature of the respective aspherical lens elements shown in Table 1
each shows a value approximate to the vertex on the lens surface of the
corresponding lens element. Also, Table 2 shows the conical coefficient k
of the aspherical surface (the i-th lens surface attached with the
asterisk (*) in Table 1), and the aspherical coefficients A, B, C, and D.

[0180]The spherical aberration (LONGITUDINAL SPHERICAL ABERRATION, the
astigmatism (ASTIGMATISM), and the distortion aberration (DISTORTION) of
the entire optical system in Example 1 having the above lens arrangement
and construction are shown in FIG. 25 from the left column to the right
column in this order. Specifically, in FIG. 25, the aberrations at the
wide angle end (W), the mid point (M), and the telephoto end (T) are
shown in the uppermost row, the intermediate row, and the lowermost row,
respectively. Each of the horizontal axes in the spherical aberration
diagrams and the astigmatism diagrams shows a focal point displacement in
the unit of mm. Each of the horizontal axes in the distortion aberration
diagrams shows a distortion with respect to the entire image in terms of
percentage. Each of the vertical axes in the spherical aberration
diagrams shows a value standardized by the incident height, and each of
the vertical axes in the astigmatism diagrams and the distortion
aberration diagrams shows a height of an optical image i.e. an image
height in the unit of mm.

[0181]In the spherical aberration diagrams, aberrations in case of using
light of three different wavelengths are shown, wherein the
one-dotted-chain lines represent aberrations in using red ray
(wavelength: 656.28 nm), the solid lines represent aberrations in using
yellow ray (so-called "d-ray" having a wavelength of 587.56 nm), and the
broken lines represent aberrations in using blue ray (wavelength: 435.84
nm). In the astigmatism diagrams, the solid lines "s" and the broken
lines "t" respectively represent displacement results on a sagittal
(radial) plane and a tangential (meridional) plane. Further, the
astigmatism diagrams and the distortion aberration diagrams show
displacement results in using yellow ray i.e. d-ray. As is obvious from
FIG. 25, the lens groups in Example 1 show superior optical
characteristics that the distortion aberration is within about 5% at any
position of the wide angle end (W), the mid point (M), and the telephoto
end (T). The focal length (unit: mm) and the F-number at the wide angle
end (W), the mid point (M), and the telephoto end (T) in Example 1 are
shown in Tables 39 and 40, respectively. Tables 39 and 40 show that
Example 1 provides a fast optical system of a short focal length.

Example 2

[0182]FIG. 7 is a cross-sectional view, taken along the optical axis (AX),
showing an arrangement of lens groups in a zoom optical system 100B as
Example 2. The zoom optical system 100B in Example 2 includes, in the
order from the object side, a first lens group (Gr1) having a negative
optical power, an aperture stop (ST) arranged on the object side of a
second lens group (Gr2), the second lens group (Gr2) having a positive
optical power as a whole, a third lens group (Gr3) having a positive
optical power, and a fourth lens group (Gr4) having a negative optical
power. More specifically, the first lens group (Gr1) is constituted of a
biconcave negative lens element (L1) and a positive meniscus lens element
(L2) convex to the object side in this order from the object side. The
second lens group (Gr2) is constituted of a biconvex positive lens
element (L3) and a biconcave negative lens element (L4). The third lens
group (Gr3) is constituted of a positive meniscus lens element (L5)
convex to the image side, and the fourth lens group (Gr4) is constituted
of a negative meniscus lens element (L6) convex to the image side.

[0183]In the zoom optical system 100B in Example 2 having the above lens
arrangement, as shown in FIG. 43, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) and the fourth lens
group (Gr4) are fixed, the second lens group (Gr2) is linearly moved
toward the object side, and the third lens group (Gr3) is linearly moved
toward the image side.

[0184]Construction data concerning the lens elements in the zoom optical
system 100B in Example 2 are shown in Tables 3 and 4. As shown in Tables
3 and 4, and FIG. 7, in Example 2, all the first through the sixth lens
elements (L1 through L6) are bi-aspherical lens elements. In the zoom
optical system 100B, the first lens element (L1), the second lens element
(L2), the fifth lens element (L5), and the sixth lens element (L6) are
resin lens elements, and the lens elements other than the above are glass
lens elements.

[0185]FIG. 8 is a cross-sectional view, taken along the optical axis (AX),
showing an arrangement of lens groups in a zoom optical system 100C as
Example 3. The zoom optical system 100C in Example 3 includes, in the
order from the object side, a first lens group (Gr1) having a negative
optical power as a whole, an aperture stop (ST) arranged on the object
side of a second lens group (Gr2), the second lens group (Gr2) having a
positive optical power as a whole, and a third lens group (Gr3) having a
positive optical power. More specifically, the first lens group (Gr1) is
constituted of a biconcave negative lens element (L1) and a positive
meniscus lens element (L2) convex to the object side in this order from
the object side. The second lens group (Gr2) is constituted of a biconvex
positive lens element (L3) and a negative lens element (L4) convex to the
object side in this order from the object side. The third lens group
(Gr3) is constituted of a positive meniscus lens element (L5) convex to
the object side.

[0186]In the zoom optical system 100C in Example 3 having the above lens
arrangement, as shown in FIG. 43, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, the
second lens group (Gr2) is linearly moved toward the object side, and the
third lens group (Gr3) is fixed. The aperture stop (ST) is moved with the
second lens group (Gr2) in zooming.

[0187]Construction data concerning the lens elements in the zoom optical
system 100C in Example 3 are shown in Tables 5 and 6. As shown in Tables
5 and 6, and FIG. 8, in Example 3, all the first through the sixth lens
elements (L1 through L6) are bi-aspherical lens elements. In the zoom
optical system 100C, the fifth lens element (L5) is a resin lens element,
and the lens elements other than the fifth lens element (L5) are glass
lens elements.

[0188]FIG. 9 is a cross-sectional view, taken along the optical axis (AX),
showing an arrangement of lens groups in a zoom optical system 100D as
Example 4. The zoom optical system 100D in Example 4 includes, in the
order from the object side, a first lens group (Gr1) having a negative
optical power as a whole, an aperture stop (ST), a second lens group
(Gr2) having a positive optical power as a whole, and a third lens group
(Gr3) having a positive optical power. More specifically, the first lens
group (Gr1) is constituted of a biconcave negative lens element (L1) and
a positive meniscus lens element (L2) convex to the object side in this
order from the object side. The second lens group (Gr2) is constituted of
a biconvex positive lens element (L3) and a biconcave negative lens
element (L4) in this order from the object side. The third lens group
(Gr3) is constituted of a biconvex positive lens element (L5). In Example
4, the aperture stop (ST) is of an aperture-stop-coated type, which is
obtained by coating the object-side lens surface of the biconvex positive
lens element (L3) with black.

[0189]In the zoom optical system 100D in Example 4 having the above lens
arrangement, as shown in FIG. 43, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, the
second lens group (Gr2) is linearly moved toward the object side, and the
third lens group (Gr3) is linearly moved toward the image side. Since the
aperture stop (ST) is of an aperture-stop-coated type, which is obtained
by coating the lens surface with black, the aperture stop (ST) is moved
with the second lens group (Gr2) in zooming.

[0190]Construction data concerning the lens elements in the zoom optical
system 100D in Example 4 are shown in Tables 7 and 8. As shown in Tables
7 and 8, and FIG. 9, in Example 4, the first lens element (L1), the
fourth lens element (L4), and the fifth lens element (L5) are
bi-aspherical lens elements, and the third lens element (L3) is a
mono-aspherical lens element having an aspherical surface on one side
thereof. In the zoom optical system 100D, all the first through the fifth
lens elements (L1 through L5) are resin lens elements.

[0191]FIG. 10 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 100E
as Example 5. The zoom optical system 100E in Example 5 includes, in the
order from the object side, a first lens group (Gr1) having a negative
optical power, an aperture stop (ST), a second lens group (Gr2) having a
positive optical power as a whole, and a third lens group (Gr3) having a
positive optical power. More specifically, the first lens group (Gr1) is
constituted of a biconcave negative lens element (L1). The second lens
group (Gr2) is constituted of a biconvex positive lens element (L3) and a
biconcave negative lens element (L3) in this order from the object side.
The third lens group (Gr3) is constituted of a biconvex positive lens
element (L4).

[0192]In the zoom optical system 100E in Example 5 having the above lens
arrangement, as shown in FIG. 44, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, the
second lens group (Gr2) is linearly moved toward the object side, and the
third lens group (Gr3) is fixed. The aperture stop (ST) is moved with the
second lens group (Gr2) in zooming.

[0193]Construction data concerning the lens elements in the zoom optical
system 100E in Example 5 are shown in Tables 9 and 10. As shown in Tables
9 and 10, and FIG. 10, in Example 5, all the first through the fourth
lens elements (L1 through L4) are bi-aspherical lens elements. In the
zoom optical system 100E, the first lens element (L1) and the fourth lens
element (L4) are resin lens elements.

[0194]FIG. 11 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 100F
as Example 6. The zoom optical system 100F in Example 6 includes, in the
order from the object side, a first lens group (Gr1) having a negative
optical power as a whole, an aperture stop (ST), a second lens group
(Gr2) having a positive optical power as a whole, and a third lens group
(Gr3) having a positive optical power. More specifically, the first lens
group (Gr1) is constituted of a biconcave negative lens element (L1) and
a positive meniscus lens element (L2) convex to the object side in this
order from the object side. The second lens group (Gr2) is constituted of
a biconvex positive lens element (L3) and a negative lens element (L4)
convex to the object side in this order from the object side. The third
lens group (Gr3) is constituted of a biconvex positive lens element (L5).

[0195]In the zoom optical system 100F in Example 6 having the above lens
arrangement, as shown in FIG. 43, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, the
second lens group (Gr2) is linearly moved toward the object side, and the
third lens group (Gr3) is moved toward the image side. The aperture stop
(ST) is moved with the second lens group (Gr2) in zooming.

[0196]Construction data concerning the lens elements in the zoom optical
system 100F in Example 6 are shown in Tables 11 and 12. As shown in
Tables 11 and 12, and FIG. 11, in Example 6, the second through the fifth
lens elements (L2 through L5) are bi-aspherical lens elements, and the
first lens element (L1) is a mono-aspherical lens element. In the zoom
optical system 100F, all the first through the fifth lens elements (L1
through L5) are glass lens elements.

[0197]FIG. 12 is a cross-sectional view, taken along the optical axis (AX)
showing an arrangement of lens groups in a zoom optical system 100G as
Example 7. The zoom optical system 100G in Example 7 includes, in the
order from the object side, a first lens group (Gr1) having a negative
optical power as a whole, an aperture stop (ST), a second lens group
(Gr2) having a positive optical power as a whole, and a third lens group
(Gr3) having a positive optical power. More specifically, the first lens
group (Gr1) is constituted of a biconcave negative lens element (L1) and
a positive meniscus lens element convex to the object side in this order
from the object side. The second lens group (Gr2) is constituted of a
biconvex positive lens element (L3) and a negative meniscus lens element
(L4) convex to the object side in this order from the object side. The
third lens group (Gr3) is constituted of a positive meniscus lens element
(L5) convex to the object side.

[0198]In the zoom optical system 100G in Example 7 having the above lens
arrangement, as shown in FIG. 43, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, the
second lens group (Gr2) is linearly moved toward the object side, and the
third lens group (Gr3) is fixed. The aperture stop (ST) is moved with the
second lens group (Gr2) in zooming.

[0199]Construction data concerning the lens elements in the zoom optical
system 100G in Example 7 are shown in Tables 13 and 14. As shown in
Tables 13 and 14, and FIG. 12, in Example 7, all the first through the
fifth lens elements (L1 through L5) are bi-aspherical lens elements. In
the zoom optical system 100G, all the first through the fifth lens
elements (L1 through L5) are glass lens elements.

[0200]FIG. 13 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 100H
as Example 8. The zoom optical system 100H in Example 8 includes, in the
order from the object side, a first lens group (Gr1) having a negative
optical power as a whole, an aperture stop (ST), a second lens group
(Gr2) having a positive optical power as a whole, and a third lens group
(Gr3) having a positive optical power. More specifically, the first lens
group (Gr1) is constituted of a cemented lens element composed of a
biconcave negative lens element (L1) and a positive meniscus lens element
(L2) convex to the object side in this order from the object side. The
second lens group (Gr2) is constituted of a cemented lens element
composed of a biconvex positive lens element (L3) and a biconcave
negative lens element (L4) in this order from the object side. The third
lens group (Gr3) is constituted of a positive meniscus lens element (L5)
convex to the image side.

[0201]In the zoom optical system 100H in Example 8 having the above lens
arrangement, as shown in FIG. 43, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, the
second lens group (Gr2) is linearly moved toward the object side, and the
third lens group (Gr3) is linearly moved toward the image side. The
aperture stop (ST) is moved with the second lens group (Gr2) in zooming.

[0202]Construction data concerning the lens elements in the zoom optical
system 100H in Example 8 are shown in Tables 15 and 16. As shown in
Tables 15 and 16, and FIG. 13, in Example 8, the first through the fourth
lens elements (L1 through L4) are each a mono-aspherical lens element,
and the fifth lens element (L5) is a biaspherical lens element. In the
zoom optical system 100H, the first lens element (L1), the second lens
element (L2), and the fifth lens element (L5) are resin lens elements,
and the lens elements other than the above are glass lens elements.

[0203]FIG. 14 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 100I
as Example 9. The zoom optical system 100I in Example 9 includes, in the
order from the object side, a first lens group (Gr1) having a negative
optical power as a whole, an aperture stop (ST), a second lens group
(Gr2) having a positive optical power as a whole, and a third lens group
(Gr3) having a positive optical power. More specifically, the first lens
group (Gr1) is constituted of a negative meniscus lens element (L1)
convex to the object side, a biconcave negative lens element (L2), and a
positive meniscus lens element (L3) convex to the object side in this
order from the object side. The second lens group (Gr2) is constituted of
a cemented lens element composed of a biconvex positive lens element (L4)
and a biconcave negative lens element (L5) in this order from the object
side. The third lens group (Gr3) is constituted of a biconvex positive
lens element (L6).

[0204]In the zoom optical system 100I in Example 9 having the above lens
arrangement, as shown in FIG. 44, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) and the second lens
group (Gr2) are linearly moved toward the object side, and the third lens
group (Gr3) is linearly moved toward the image side. The aperture stop
(ST) is moved with the second lens group (Gr2) in zooming.

[0205]Construction data concerning the lens elements in the zoom optical
system 100I in Example 9 are shown in Tables 17 and 18. As shown in
Tables 17 and 18, and FIG. 14, in Example 9, the fourth through the sixth
lens elements (L4 through L6) are each a mono-aspherical lens element. In
the zoom optical system 100I, all the first through the sixth lens
elements (L1 through L6) are glass lens elements.

[0206]FIG. 15 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 100J
as Example 10. The zoom optical system 100J in Example 10 includes, in
the order from the object side, a first lens group (Gr1) having a
negative optical power as a whole, an aperture stop (ST), a second lens
group (Gr2) having a positive optical power as a whole, and a third lens
group (Gr3) having a positive optical power. More specifically, the first
lens group (Gr1) is constituted of a negative meniscus lens element (L1)
convex to the object side and a positive meniscus lens element (L2)
convex to the object side in this order from the object side. The second
lens group (Gr2) is constituted of a biconvex positive lens element (L3)
and a negative meniscus lens element (L4) convex to the object side in
this order from the object side. The third lens group (Gr3) is
constituted of a positive meniscus lens element (L5) convex to the object
side.

[0207]In the zoom optical system 100J in Example 10 having the above lens
arrangement, as shown in FIG. 43, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, the
second lens group (Gr2) is linearly moved toward the object side, and the
third lens group (Gr3) is fixed. The aperture stop (ST) is moved with the
second lens group (Gr2) in zooming.

[0208]Construction data concerning the lens elements in the zoom optical
system 100J in Example 10 are shown in Tables 19 and 20. As shown in
Tables 19 and 20, and FIG. 15, in Example 10, the second through the
fifth lens elements (L2 through L5) are each a bi-aspherical lens
element, and the first lens element (L1) is a mono-aspherical lens
element. The first lens element (L1) is a composite aspherical lens
element. In the zoom optical system 100J, all the first through the fifth
lens elements (L1 through L5) are glass lens elements.

[0209]FIG. 16 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 100K
as Example 11. The zoom optical system 100K in Example 11 includes, in
the order from the object side, a first lens group (Gr1) having a
negative optical power as a whole, an aperture stop (ST), a second lens
group (Gr2) having a positive optical power as a whole, a third lens
group (Gr3) having a negative optical power, and a fourth lens group
(Gr4) having a positive optical power. More specifically, the first lens
group (Gr1) is constituted of a biconcave negative lens element (L1) and
a positive meniscus lens element (L2) convex to the object side in this
order from the object side. The second lens group (Gr2) is constituted of
a biconvex positive lens element (L3) and a biconcave negative lens
element (L4) in this order from the object side. The third lens group
(Gr3) is constituted of a negative meniscus lens element (L5) convex to
the object side. The fourth lens group (Gr4) is constituted of a biconvex
positive lens element (L6).

[0210]In the zoom optical system 100K in Example 11 having the above lens
arrangement, as shown in FIG. 44, in zooming from the wide angle end (W)
to the telephoto end (T), the second lens group (Gr2) is linearly moved
toward the object side, and the third lens group (Gr3) makes a U-turn.
The first lens group (Gr1) and the fourth lens group (Gr4) are fixed. The
aperture stop (ST) is moved with the second lens group (Gr2) in zooming.

[0211]Construction data concerning the lens elements in the zoom optical
system 100K in Example 11 are shown in Tables 21 and 22. As shown in
Tables 21 and 22, and FIG. 16, in Example 11, all the first through the
sixth lens elements (L1 through L6) are each a bi-aspherical lens
element. In the zoom optical system 100K, the first lens element (L1),
the fifth lens element (L5), and the sixth lens element (L6) are resin
lens elements, and the lens elements other than the above are glass lens
elements.

[0212]FIG. 17 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 100L
as Example 12. The zoom optical system 100L in Example 12 includes, in
the order from the object side, a first lens group (Gr1) having a
negative optical power as a whole, an aperture stop (ST), a second lens
group (Gr2) having a positive optical power as a whole, and a third lens
group (Gr3) having a positive optical power. More specifically, the first
lens group (Gr1) is constituted of a biconcave negative lens element (L1)
and a positive meniscus lens element (L2) convex to the object side in
this order from the object side. The second lens group (Gr2) is
constituted of a biconvex positive lens element (L3) and a biconcave
negative lens element (L4) in this order from the object side. The third
lens group (Gr3) is constituted of a positive meniscus lens element (L5)
convex to the image side. In Example 12, the aperture stop (ST) is of an
aperture-stop-coated type, which is obtained by coating the object-side
lens surface of the biconvex positive lens element (L3) with black.

[0213]In the zoom optical system 100L in Example 12 having the above lens
arrangement, as shown in FIG. 43, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, the
second lens group (Gr2) is linearly moved toward the object side, and the
third lens group (Gr3) is fixed. The aperture stop (ST) is moved with the
second lens group (Gr2) in zooming.

[0214]Construction data concerning the lens elements in the zoom optical
system 100L in Example 12 are shown in Tables 23 and 24. As shown in
Tables 23 and 24, and FIG. 17, in Example 12, the first lens element
(L1), the fourth lens element (L4), and the fifth lens element (L5) are
each a bi-aspherical lens element, and the third lens element (L3) is a
mono-aspherical lens element. In the zoom optical system 100L, all the
first through the fifth lens elements (L1 through L5) are resin lens
elements.

[0215]FIG. 18 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 100M
as Example 13. The zoom optical system 100M in Example 13 includes, in
the order from the object side, a first lens group (Gr1) having a
negative optical power as a whole, an aperture stop (ST), a second lens
group (Gr2) having a positive optical power as a whole, and a third lens
group (Gr3) having a positive optical power. More specifically, the first
lens group (Gr1) is constituted of a biconcave negative lens element (L1)
and a positive meniscus lens element (L2) convex to the object side in
this order from the object side. The second lens group (Gr2) is
constituted of a biconvex positive lens element (L3) and a negative
meniscus lens element (L4) convex to the object side in this order from
the object side. The third lens group (Gr3) is constituted of a biconvex
positive lens element (L5).

[0216]In the zoom optical system 100M in Example 13 having the above lens
arrangement, as shown in FIG. 44, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, and
the second lens group (Gr2) and the third lens group (Gr3) are linearly
moved toward the object side. The aperture stop (ST) is moved with the
second lens group (Gr2) in zooming.

[0217]Construction data concerning the lens elements in the zoom optical
system 100M in Example 13 are shown in Tables 25 and 26. As shown in
Tables 25 and 26, and FIG. 18, in Example 13, all the first through the
fifth lens elements (L1 through L5) are each a bi-aspherical lens
element. In the zoom optical system 100M, the first lens element (L1),
the second lens element (L2), and the fifth lens element (L5) are resin
lens elements, and the lens elements other than the above are glass lens
elements.

[0218]FIG. 19 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 100N
as Example 14. The zoom optical system 100N in Example 14 includes, in
the order from the object side, a first lens group (Gr1) having a
negative optical power as a whole, an aperture stop (ST), a second lens
group (Gr2) having a positive optical power as a whole, and a third lens
group (Gr3) having a positive optical power. More specifically, the first
lens group (Gr1) is constituted of a biconcave negative lens element (L1)
and a positive meniscus lens element (L2) convex to the object side in
this order from the object side. The second lens group (Gr2) is
constituted of a biconvex positive lens element (L3) and a negative
meniscus lens element (L4) convex to the object side in this order from
the object side. The third lens group (Gr3) is constituted of a biconvex
positive lens element (L5).

[0219]In the zoom optical system 100N in Example 14 having the above lens
arrangement, as shown in FIG. 43, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, the
second lens group (Gr2) is linearly moved toward the object side, and the
third lens group (Gr3) is fixed. The aperture stop (ST) is moved with the
second lens group (Gr2) in zooming.

[0220]Construction data concerning the lens elements in the zoom optical
system 100N in Example 14 are shown in Tables 27 and 28. As shown in
Tables 27 and 28, and FIG. 19, in Example 14, the second through the
fifth lens elements (L2 through L5) are each a bi-aspherical lens
element, and the first lens element (L1) is a mono-aspherical lens
element. In the zoom optical system 100N, the second lens element (L2)
and the fifth lens element (L5) are resin lens elements, and the lens
elements other than the above are glass lens elements.

[0221]FIG. 20 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 1000
as Example 15. The zoom optical system 1000 in Example 15 includes, in
the order from the object side, a first lens group (Gr1) having a
negative optical power as a whole, an aperture stop (ST), a second lens
group (Gr2) having a positive optical power as a whole, and a third lens
group (Gr3) having a positive optical power. More specifically, the first
lens group (Gr1) is constituted of a biconcave negative lens element (L1)
and a positive meniscus lens element (L2) convex to the object side in
this order from the object side. The second lens group (Gr2) is
constituted of a biconvex positive lens element (L3) and a negative
meniscus lens element (L4) convex to the object side in this order from
the object side. The third lens group (Gr3) is constituted of a biconvex
positive lens element (L5).

[0222]In the zoom optical system 1000 in Example 15 having the above lens
arrangement, as shown in FIG. 43, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, the
second lens group (Gr2) is linearly moved toward the object side, and the
third lens group (Gr3) is fixed. The aperture stop (ST) is moved with the
second lens group (Gr2) in zooming.

[0223]Construction data concerning the lens elements in the zoom optical
system 1000 in Example 15 are shown in Tables 29 and 30. As shown in
Tables 29 and 30, and FIG. 20, in Example 15, all the first through the
fifth lens elements (L1 through L5) are each a bi-aspherical lens
element. In the zoom optical system 1000, the first lens element (L1),
the second lens element (L2), and the fifth lens element (L5) are resin
lens elements, and the lens elements other than the above are glass lens
elements.

[0224]FIG. 21 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 100P
as Example 16. The zoom optical system 100P in Example 16 includes, in
the order from the object side, a first lens group (Gr1) having a
negative optical power as a whole, an aperture stop (ST), a second lens
group (Gr2) having a positive optical power as a whole, and a third lens
group (Gr3) having a positive optical power. More specifically, the first
lens group (Gr1) is constituted of a biconcave negative lens element (L1)
and a positive meniscus lens element (L2) convex to the object side in
this order from the object side. The second lens group (Gr2) is
constituted of a biconvex positive lens element (L3) and a negative
meniscus lens element (L4) convex to the object side in this order from
the object side. The third lens group (Gr3) is constituted of a biconvex
positive lens element (L5).

[0225]In the zoom optical system 100P in Example 16 having the above lens
arrangement, as shown in FIG. 43, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) makes a U-turn, the
second lens group (Gr2) is linearly moved toward the object side, and the
third lens group (Gr3) is fixed. The aperture stop (ST) is moved with the
second lens group (Gr2) in zooming.

[0226]Construction data concerning the lens elements in the zoom optical
system 100P in Example 16 are shown in Tables 31 and 32. As shown in
Tables 31 and 32, and FIG. 21, in Example 16, the second through the
fifth lens elements (L2 through L5) are each a bi-aspherical lens
element, and the first lens element (L1) is a mono-aspherical lens
element. In the zoom optical system 100P, all the first through the fifth
lens elements (L1 through L5) are glass lens elements.

[0227]FIG. 22 is a cross-sectional view, taken along the optical axis
(AX), showing an arrangement of lens groups in a zoom optical system 100Q
as Example 17. The zoom optical system 100Q in Example 17 includes, in
the order from the object side, a first lens group (Gr1) having a
negative optical power as a whole, an aperture stop (ST), a second lens
group (Gr2) having a positive optical power as a whole, a third lens
group (Gr3) having a negative optical power, and a fourth lens group
(Gr4) having a positive optical power. More specifically, the first lens
group (Gr1) is constituted of a negative meniscus lens element (L1)
convex to the object side and a positive meniscus lens element (L2)
convex to the object side in this order from the object side. The second
lens group (Gr2) is constituted of a biconvex positive lens element (L3),
and a cemented lens element composed of a biconcave negative lens element
(L4) and a biconvex positive lens element (L5) in this order from the
object side. The third lens group (Gr3) is constituted of a biconcave
negative lens element (L6). The fourth lens group (Gr4) is constituted of
a biconvex positive lens element (L7)

[0228]In the zoom optical system 100Q in Example 17 having the above lens
arrangement, as shown in FIG. 45, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) and the fourth lens
group (Gr4) are fixed, and the second lens group (Gr2) and the third lens
group (Gr3) are linearly moved toward the object side. The aperture stop
(ST) is moved with the second lens group (Gr2) in zooming.

[0229]Construction data concerning the lens elements in the zoom optical
system 100Q in Example 17 are shown in Tables 33 and 34. As shown in
Tables 33 and 34, and FIG. 22, in Example 17, the first through the third
lens elements (L1 through L3), the sixth lens element (L6), and the
seventh lens element (L7) are each a bi-aspherical lens element, the
fourth lens element (L4) is a spherical lens element, and the fifth lens
element (L5) is a mono-aspherical lens element. In the zoom optical
system 100Q, all the first through the seventh lens elements (L1 through
L7) are glass lens elements.

[0230]FIGS. 23 and 24 are cross-sectional views, taken along the optical
axis (AX), showing an arrangement of lens groups in a zoom optical system
100R as Example 18. The zoom optical system 100R is a bent optical system
whose optical axis (AX) is bent by 90 degrees. FIG. 23 shows an optical
arrangement of the zoom optical system 100R, and FIG. 24 is an optical
path diagram, in which the optical path of the optical arrangement shown
in FIG. 23 is converted into a linear optical path.

[0231]The zoom optical system 100R includes, in the order from the object
side, a first lens group (Gr1) having a negative optical power as a
whole, an aperture stop (ST), a second lens group (Gr2) having a positive
optical power as a whole, a third lens group (Gr3) having a negative
optical power, and a fourth lens group (Gr4) having a positive optical
power. More specifically, the first lens group (Gr1) is constituted of a
negative meniscus lens element (L1) convex to the object side, a prism
(PR) for bending the optical path by 90 degrees, and a positive meniscus
lens element (L2) convex to the object side in this order from the object
side. The second lens group (Gr2) is constituted of a biconvex positive
lens element (L3) and a negative meniscus lens element (L4) convex to the
object side in this order from the object side. The third lens group
(Gr3) is constituted of a biconcave negative lens element (L5). The
fourth lens group (Gr4) is constituted of a biconvex positive lens
element (L6).

[0232]In the zoom optical system 100R in Example 18 having the above lens
arrangement, as shown in FIG. 45, in zooming from the wide angle end (W)
to the telephoto end (T), the first lens group (Gr1) and the fourth lens
group (Gr4) are fixed, and the second lens group (Gr2) and the third lens
group (Gr3) are linearly moved toward the object side. The aperture stop
(ST) is moved with the second lens group (Gr2) in zooming.

[0233]Construction data concerning the lens elements in the zoom optical
system 100R in Example 18 are shown in Tables 35 and 36. As shown in
Tables 35 and 36, and FIGS. 23 and 24, in Example 18, the second through
the sixth lens elements (L2 through L6) are each a bi-aspherical lens
element, and the first lens element (L1) is a mono-aspherical lens
element. In the zoom optical system 100R, all the first through the sixth
lens elements (L1 through L6) are glass lens elements. In Example 18, the
prism (PR) is used to suppress the dimension of the zoom optical system
in thickness direction. The member for bending the optical path is not
limited to the prism (PR). As far as the production cost increase can be
suppressed, other equivalent element such as a reflective mirror may be
used.

[0234]FIGS. 26 through 42 each shows spherical aberration, astigmatism,
and distortion aberration of all the optical systems in Examples 2
through 18 having the aforementioned lens arrangements and constructions.
Similarly to FIG. 25, the spherical aberration diagrams in FIGS. 26
through 42 show aberrations in the case where three rays of different
wavelengths are used. Specifically, the one-dotted-chain lines represent
aberrations in using red ray, the solid lines represent aberrations in
using yellow ray, and the broken lines represent aberrations in using
blue ray. The lens groups in all Examples 2 through 18 show superior
optical characteristics that the distortion aberration is within about 5%
at any position of the wide angle end (W), the mid point (M), and the
telephoto end (T).

[0235]Also, the values of the conditional expressions (1) through (16) in
the case where the conditional expressions (1) through (16) are applied
to the optical systems in Example 2 through 18 are shown in Tables 37 and
38.

[0236]The focal length (unit: mm) and the F-number at the wide angle end
(W), the mid point (M), and the telephoto end (T) in the zoom optical
systems in Examples 2 through 18 are shown in Tables 39 and 40,
respectively. Similarly to Example 1, Tables 39 and 40 show that the zoom
optical systems in Examples 2 through 18 each provides a fast optical
system of a short focal length.

[0237]As described above, according to the zoom optical systems 100A
through 100R in Examples 1 through 18, particularly the zoom optical
system whose zoom ratio is about two to three times is advantageous in
desirably correcting various aberrations in the entire zoom range, and
providing a zoom lens device capable of realizing miniaturization or
microminiaturization with a less cost.

[0238]The foregoing embodiment and/or modifications primarily include the
inventions having the following arrangements.

[0239]A zoom optical system according to an aspect of the invention
includes a first lens group having a negative optical power, a second
lens group having a positive optical power, and a third lens group having
a positive or negative optical power in this order from an object side.
The zoom optical system is configured in such a manner that an interval
between the first lens group and the second lens group is decreased in
zooming from a wide angle end to a telephoto end, wherein a positive lens
element in the third lens group or in a lens group closer to an image
side than the third lens group satisfies the following conditional
expression (1):

vp<40 (1)

where vp is a minimum value of the Abbe number of the positive lens
element.

[0240]In the above arrangement, the zoom optical system is configured into
a negative dominant optical system, in which the first lens group closest
to the object side has a negative optical power. This enables to promptly
alleviate emission of light rays incident from the object side with a
large angle by the negative optical power of the first lens group. This
is advantageous in reducing the entire length of the optical system or
the diameter of the forwardmost lens element. Also, in the negative
dominant arrangement, increase of error sensitivity can be suppressed
despite miniaturization of the optical system. These advantages are
particularly increased in a zoom lens device whose zoom ratio is about
two to three times.

[0241]If, however, miniaturization of the optical system further
progresses, the optical power required for the individual lens elements
constituting the second lens group in the aforementioned lens arrangement
is increased. As a result, magnification chromatic aberration at the
telephoto end may be unduly increased. In view of this, the positive lens
element in the third lens group or in the lens group closer to the image
side than the third lens group is made of a high dispersive material
having the Abbe number satisfying the aforementioned conditional
expression (1) to correct the aberration. If the Abbe number is over the
upper limit in the conditional expression (1), correction of
magnification chromatic aberration by the positive lens element is
insufficient, which may lower the contrast, and resultantly cause image
degradation.

[0242]The zoom optical system according to the one aspect of the invention
enables to miniaturize the zoom optical system as a negative dominant
arrangement, and sufficiently correct magnification chromatic aberration
or a like drawback in the second lens group, which may be involved in
miniaturizing or microminiaturizing the zoom optical system, by
optimizing the Abbe number of the positive lens element in the third lens
group or in the lens group closer to the image side than the third lens
group. The arrangement is advantageous in providing a satisfactorily
miniaturized zoom optical system whose aberration is desirably corrected
in the entire zoom range in a zoom optical system with a certain zoom
ratio, particularly, in a zoom optical system with a zoom ratio of about
two to three times.

[0243]Preferably, in the zoom optical system, the positive lens element
having the Abbe number may satisfy the following conditional expression
(2):

Npg>1.7 (2)

where Npg is a refractive index of the positive lens element with respect
to d-ray.

[0244]In the case where a light receiving surface of an image sensor or a
like device for converting an optical image into an electric signal is
disposed on the image side of the zoom optical system, the positive lens
element in the lens group including the third lens group and thereafter
serves as a member for adjusting the incident angle of an incident ray to
be guided to the image sensor. In view of this, a difference in incident
angle with respect to the image sensor between the wide angle end and the
telephoto end can be reduced, and production feasibility can be increased
by using the high refractive glass material satisfying the conditional
expression (2) as a material for the positive lens element. If the
refractive index of the positive lens element is under the lower limit in
the conditional expression (2), the plane angle of the third lens group
or the lens group closer to the image side than the third lens group may
be increased. Particularly, in case of a glass lens element, production
requirement or assessment on lens performance is severe, which may
increase the production cost. As described above, in the case where the
light receiving surface of the image sensor is disposed on the image side
of the zoom optical system, optimizing the refractive index of the
positive lens element in the lens group including the third lens group
and thereafter is advantageous in reducing the difference in incident
angle with respect to the image sensor between the wide angle end and the
telephoto end, and increasing production feasibility of the zoom optical
system.

[0245]Preferably, in the zoom optical system, the positive lens element
having the Abbe number may be made of a resin material, and may satisfy
the following conditional expression (3):

Npp>1.55 (3)

where Npp is a refractive index of the positive lens element made of the
resin material with respect to d-ray.

[0246]In the zoom optical system, it is desirable to compose the lens
element constituting the optical system of a resin material in the aspect
of production cost and mass-productivity. In this case, using the resin
material having the refractive index satisfying the conditional
expression (3) for the positive lens element in the lens group including
the third lens group and thereafter enables to produce an optical system
capable of sufficiently correcting magnification chromatic aberration or
the like. If the refractive index of the positive lens element is under
the lower limit in the conditional expression (3), the material for the
positive lens element is limited to a low dispersive material, which may
obstruct sufficient correction of magnification chromatic aberration.

[0247]In the zoom optical system, preferably, the positive lens element
having the Abbe number may have at least one aspherical surface. In this
arrangement, astigmatism/distortion aberration can be sufficiently
corrected by forming at least one aspherical surface in the positive lens
element. Also, this arrangement enables to increase latitude in adjusting
the incident angle of an optical image with respect to the image sensor,
and reduce a difference in incident angle with respect to the image
sensor between the wide angle end and the telephoto end. Thus, the
arrangement is advantageous in obtaining an image in which a sufficient
light amount is secured even in the periphery of the image.

[0248]It is difficult to form an aspherical surface in a glass lens
element, as compared with a plastic lens element. Generally, as the
refractive index of a glass lens element is increased, the melting point
thereof is increased, which makes it difficult to form an aspherical
surface in the glass lens element. The high dispersive material to be
used in the invention i.e. the material defined by the conditional
expression (1) has a low melting point despite a relatively high
refractive index. The high dispersive material is relatively easily
moldable by a glass molding process or a like process even in use of the
glass material for the positive lens element. Thus, this arrangement is
advantageous in forming an aspherical surface in the glass lens element.

[0249]In the zoom optical system, preferably, the second lens group may
satisfy the following conditional expression (4):

0.7<f2/fw<2.0 (4)

where f2 is a composite focal length of the second lens group, and fw is a
composite focal length of the entirety of the zoom optical system at the
telephoto end.

[0250]In the zoom optical system satisfying the conditional expression
(4), an intended zoom ratio can be obtained while securing
miniaturization. If f2/fw is over the upper limit in the conditional
expression (4), the power of the second lens group may be weakened, which
makes it difficult to obtain a zoom ratio of about two to three times,
while keeping miniaturization. On the other hand, if f2/fw is under the
lower limit in the conditional expression (4), decentering error
sensitivity of the second lens group may be unduly increased, which makes
it difficult to produce lens groups with no or less error sensitivity.
Optimizing the value of f2/fw as mentioned above is advantageous in
obtaining an intended zoom ratio while securing miniaturization.

[0251]In the zoom optical system, preferably, the zoom optical system may
satisfy the following conditional expressions (5) and (6):

0<αw<30 (5)

|αw-αt|<20 (6)

where αw is an angle (deg) of a principal ray, at a maximum image
height, of incident rays onto an imaging surface with respect to a normal
to an imaging plane at the wide angle end, and αt is an angle (deg)
of the principal ray, at the maximum image height, of the incident rays
onto the imaging surface with respect to the normal to the imaging plane
at the telephoto end, based on a premise that the angle of the principal
ray in the case where an exit pupil position is on the object side with
respect to the imaging plane is in a plus direction.

[0252]Under the condition that the image sensor is disposed on the image
side, if αw is over the upper limit in the conditional expression
(5), intended telecentricity cannot be secured for the incident angle of
the incident ray with respect to the image sensor. Even if a lens array
corresponding to the pixels of the image sensor is arranged in front of
the imaging surface of the image sensor, it is difficult to prevent
lowering of peripheral illuminance. Setting the value of αw in such
a manner that αw does not exceed the lower limit in the conditional
expression (5) enables to attain miniaturization while securing a wide
angle of view. On the other hand, if |αw-αt| is over the
upper limit in the conditional expression (6), a difference in incident
angle between the wide angle end and the telephoto end may be unduly
increased, which makes it difficult to optimize the lens array. As a
result, peripheral illuminance may likely to be reduced at the wide angle
end or the telephoto end. In view of this, the above arrangement is
advantageous in suppressing a likelihood that peripheral illuminance with
respect to the image sensor may be reduced, and capturing a high-quality
image while securing miniaturization.

[0253]Preferably, the zoom optical system may be constituted merely of the
first lens group, the second lens group, and the third lens group, and
the third lens group may be constituted of a positive lens element.

[0254]In microminiaturizing the zoom optical system, the space occupied
ratio of the lens elements relative to the entire space for the lens unit
is relatively increased, because the lens elements necessarily occupy a
certain space, considering production constraints. Therefore, the number
of lens groups or the number of lens elements is required to be reduced
as much as possible despite the need of improving precision of individual
lens elements. In view of this, configuring the lens groups into a
three-component unit of negative-positive-positive arrangement in this
order from the object side enables to optimize the balance concerning
performances as the zoom optical system such as focusing performance,
production error sensitivity, and telecentricity for the incident angle
with respect to the imaging plane, while advantageously attaining
miniaturization of the zoom optical system, as compared with the
conventional zoom optical systems. In the three-component zoom optical
system, it is relatively easy to constitute the third lens group of a
single lens element, because the third lens group has a smaller optical
power than the first lens group or the second lens group. This is further
advantageous in attaining miniaturization.

[0255]In the above arrangement, preferably, the third lens group may be
fixed in zooming from the wide angle end to the telephoto end. With this
arrangement, since the third lens group is fixed in zooming, the lens
barrel mechanism can be simplified, and position precision of the lens
elements can be improved. This enables to provide an arrangement suitable
for microminiaturizing the zoom optical system.

[0256]In the zoom optical system, preferably, the third lens group may
have a negative optical power, and the zoom optical system may include a
fourth lens group which is arranged on the image side of the third lens
group and which has a positive optical power. With this arrangement,
since the third lens group has a negative optical power, axial chromatic
aberration can be sufficiently corrected. This enables to enhance the
contrast at the center of a captured image on a display screen. Also,
since the fourth lens group is provided in the zoom optical system,
intended optical performance with respect to a close object can be easily
secured.

[0257]In the above arrangement, preferably, the positive lens element
having the Abbe number may be included in the fourth lens group. The
fourth lens group closer to the image side is located at such a position
that the principal ray height of an off-axis ray is set high. Using the
positive lens element having the Abbe number as the positive lens element
in the fourth lens group is advantageous in correcting magnification
chromatic aberration.

[0258]In the above arrangement, preferably, the fourth lens group may be
constituted of a positive lens element. In the four-component zoom
optical system, since the fourth lens group has a smaller optical power
than the first lens group or the second lens group, it is relatively easy
to constitute the fourth lens group of a single lens element. This is
further advantageous in miniaturizing the zoom optical system.

[0259]In the arrangement that the third lens group has a negative optical
power, and the fourth lens group has a positive optical power,
preferably, the fourth lens group may be fixed in zooming from the wide
angle end to the telephoto end. Since the fourth lens group is fixed in
zooming, the lens barrel mechanism can be simplified, and position
precision of the lens elements can be improved.

[0260]In the arrangement that the third lens group has a negative optical
power, and the fourth lens group has a positive optical power,
preferably, the first lens group may be fixed in zooming from the wide
angle end to the telephoto end. The first lens group whose outer diameter
is inherently large greatly affects the dimensions of the zoom optical
system as a lens unit. In this arrangement, since the first lens group is
fixed in zooming, the lens barrel mechanism can be simplified, which is
advantageous in miniaturizing the zoom optical system in length, width,
and thickness directions.

[0261]In the arrangement that the third lens group has a negative optical
power, and the fourth lens group has a positive optical power, both of
the first lens group and the fourth lens group are fixed in zooming from
the wide angle end to the telephoto end, the weight of the lens groups to
be driven in zooming with use of the four-component zoom optical system
can be maximally reduced. This allows for use of a small-sized driving
device as a zoom mechanism, which is further advantageous in
miniaturizing the zoom optical system as a lens unit.

[0262]In the zoom optical system, preferably, the third lens group may
have a positive optical power, and the zoom optical system may include a
fourth lens group which is arranged on the image side of the third lens
group and which has a negative optical power. With this arrangement,
since the third lens group has a positive optical power, the incident
angle of the incident ray with respect to the image sensor disposed on
the imaging plane is allowed to have adequate telecentricity. Also, since
the fourth lens group is provided in the zoom optical system, intended
optical performance with respect to a close object can be easily secured.

[0263]In the above arrangement, preferably, the positive lens element
having the Abbe number may be included in the third lens group. The third
lens group closer to the image side is located at such a position that
the principal ray height of an off-axis ray is set high. Using the
positive lens element having the Abbe number as the positive lens element
in the third lens group is advantageous in correcting magnification
chromatic aberration.

[0264]In the above arrangement, preferably, the third lens group may be
constituted of a positive lens element. In the four-component zoom
optical system, since the third lens group has a smaller optical power
than the first lens group or the second lens group, it is relatively easy
to constitute the third lens group of a single lens element. This is
further advantageous in miniaturizing the zoom optical system.

[0265]In the arrangement that the third lens group has a positive optical
power, and the fourth lens group has a negative optical power,
preferably, the fourth lens group may be fixed in zooming from the wide
angle end to the telephoto end. Since the fourth lens group is fixed in
zooming, the lens barrel mechanism can be simplified, and position
precision of the lens elements can be improved.

[0266]In the arrangement that the third lens group has a positive optical
power, and the fourth lens group has a negative optical power,
preferably, the first lens group may be fixed in zooming from the wide
angle end to the telephoto end. The first lens group whose outer diameter
is inherently large greatly affects the dimensions of the zoom optical
system as a lens unit. Since the first lens group is fixed in zooming,
the lens barrel mechanism can be simplified, which is advantageous in
miniaturizing the zoom optical system in length, width, and thickness
directions.

[0267]In the arrangement that the third lens group has a positive optical
power, and the fourth lens group has a negative optical power, if both of
the first lens group and the fourth lens group are fixed in zooming from
the wide angle end to the telephoto end, the weight of the lens groups to
be driven in zooming with use of the four-component zoom optical system
can be maximally reduced. This allows for use of a small-sized driving
device as a zoom mechanism, which is further advantageous in
miniaturizing the zoom optical system as a lens unit.

[0268]In the zoom optical system, preferably, the second lens group may be
constituted of a positive lens element and a negative lens element in
this order from the object side, and may satisfy the following
conditional expression (7):

0.7<|f2n/f2p|<1.8 (7)

where f2n is a focal length of the negative lens element in the second
lens group, and f2p is a focal length of the positive lens element in the
second lens group.

[0269]In the above arrangement, since the second lens group is constituted
of a positive lens element and a negative lens element, and f2n/f2p
satisfies the conditional expression (7), spherical aberration and axial
chromatic aberration can be sufficiently corrected by the positive lens
element and the negative lens element. Also, since the positive lens
element and the negative lens element are arranged in this order from the
object side, the principal point position of the second lens group can be
approximated toward the first lens group. This enables to reduce the
substantial power of the second lens group while keeping the zoom
function, which is advantageous in reducing error sensitivity. If f2n/f2p
is over the upper limit in the conditional expression (7), spherical
aberration correction is insufficient. On the other hand, if f2n/f2p is
under the lower limit in the conditional expression (7), the optical
power of the negative lens element in the second lens group may be unduly
increased, which may increase magnification chromatic aberration and
degrade the image quality.

[0270]Preferably, the zoom optical system may further comprise an aperture
stop on the object side of the second lens group, wherein the aperture
stop has a fixed aperture diameter. In this arrangement, the diameter of
the forwardmost lens element in the first lens group can be maximally
reduced by arranging the aperture stop whose aperture diameter is fixed
on the object side of the second lens group. The interval between the
first lens group and the second lens group greatly affects the entire
length of the optical system. Accordingly, increasing the interval for
providing a variable aperture mechanism between the first lens group and
the second lens group may increase the entire length of the optical
system by about two to three times, for instance. In the above
arrangement, since the aperture diameter is fixed, the construction of
the aperture member can be simplified, thereby enabling to reduce the
size of the optical system in the optical axis direction. Thus, the
arrangement is advantageous in reducing the size of the zoom optical
system in the thickness direction.

[0271]In the zoom optical system, preferably, the positive lens element
having the Abbe number may be a meniscus lens element convex to the
object side. In this arrangement, since the principal point position of
the lens element can be set away from the imaging plane, the incident
angle of the incident ray with respect to the imaging plane can be
reduced. Thus, this arrangement is advantageous in microminiaturizing the
zoom optical system.

[0272]In the zoom optical system, preferably, an image-side lens surface
of the positive lens element having the Abbe number may be aspherical,
and the image-side lens surface of the positive lens element may satisfy
the following conditional expression (8):

0.05<|ΔZpi/di|<0.25 (8)

where ΔZpi is an amount of aspherical sag, at a maximum effective
radius, of the image-side lens surface of the positive lens element
having the Abbe number, and di is the maximum effective radius of the
image-side lens surface of the positive lens element having the Abbe
number.

[0273]In the above arrangement, the value of ΔZpi/di is optimized.
If ΔZpi/di is over the upper limit in the conditional expression
(8), the plane angle at a periphery of the lens element may be unduly
increased, which makes it difficult to produce an intended zoom optical
system, or provide product assessment. On the other hand, if
ΔZpi/di is under the lower limit in the conditional expression (8),
it is impossible to reduce a difference in incident angle with respect to
the image sensor between the wide angle end and the telephoto end, which
may lower the peripheral illuminance. Further, forming the image-side
lens surface of the positive lens element into an aspherical shape is
particularly advantageous in correcting distortion aberration. Thus, the
arrangement enables to properly set the plane angle at the periphery of
the lens element, and suppress lowering of the peripheral illuminance.

[0274]In the zoom optical system, preferably, the positive lens element
having the Abbe number may satisfy the following conditional expression
(9):

1<fp/fw<8 (9)

where fp is a focal length of the positive lens element having the Abbe
number.

[0275]In the above arrangement, since the value of fp/fw is optimized,
magnification chromatic aberration can be further advantageously
corrected, which makes it possible to obtain a high-quality image. If
fp/fw is over the upper limit in the conditional expression (9),
magnification chromatic aberration correction is insufficient. On the
other hand, if fp/fw is under the lower limit in the conditional
expression (9), magnification chromatic aberration correction is
excessive. In both of the cases, image-quality at the periphery of the
captured image is considerably degraded.

[0276]In the zoom optical system, preferably, the first lens group may be
constituted of a biconcave lens element or a negative meniscus lens
element convex to the object side, and of a positive meniscus lens
element convex to the object side in this order from the object side.
Configuring the lens arrangement of the first lens group in the
aforementioned manner enables to easily secure a long back focus distance
at the wide angle end, and desirably correct astigmatism and
magnification chromatic aberration of an off-axis ray with a wide angle
of view. Also, since the positive meniscus lens element convex to the
object side is arranged in the first lens group, astigmatism can be
desirably corrected, which enables to improve the quality of an image.

[0277]In the zoom optical system, preferably, focusing from an infinite
object distance to a close object distance may be performed by moving the
first lens group to the object side. Change in various aberrations
resulting from moving the first lens group is relatively small.
Accordingly, performance degradation by focusing can be suppressed by
moving the first lens group to the object side for focusing. Also, since
large back focus change relative to the moving amount of the first lens
group is secured, it is possible to obtain desirable focusing performance
up to a position close to the lens element by about several centimeters
with a less moving amount.

[0278]In the zoom optical system, preferably, focusing from an infinite
object distance to a close object distance may be performed by moving the
third lens group or the lens group closer to the image side than the
third lens group to the object side. This arrangement enables to obtain a
clear image up to a close object distance by moving the third lens group
or the lens group closer to the image side than the third lens group for
focusing without likelihood that the entire length of the optical system
by protrusion of a lens barrel, or the diameter of the forwardmost lens
element may be unduly increased.

[0279]Judgment as to whether the first lens group, or the third lens group
or the lens group closer to the image side than the third lens group is
to be moved in focusing is determined depending on the optical
specifications of the zoom optical system. Specifically, the first lens
group is moved in activating the macro function, and the third lens group
or the lens group closer to the image side than the third lens group is
moved in prioritizing miniaturization of the zoom optical system.

[0280]In the zoom optical system, preferably, the second lens group may
include a cemented lens element. If the size of the zoom optical system
in the optical axis direction is reduced, the moving amount of the second
lens group is restricted. Under the above condition, it is necessary to
increase the optical power of the second lens group so as to obtain an
intended zoom ratio. As a result, sensitivities with respect to curvature
error of the lens elements, center thickness error of the lens elements,
refractive index error of the lens elements, interval error between the
lens elements, and decentering error of the lens elements are increased,
which may necessitate improvement in mechanical precision of the lens
barrel or adjustment between the lens elements in the second lens group.
In the above arrangement, since the cemented lens element is included in
the second lens group, error sensitivities of the lens elements in the
second lens group can be remarkably reduced. Even in need of adjustment
between the lens elements, sensitivity balance can be desirably retained.
Also, this arrangement enables to simplify the lens barrel construction
of the second lens group. Accordingly, unlike the conventional
arrangement in which a larger space for the optical system is necessary
because of mechanical constraints despite an optical disadvantage, the
space for the zoom optical system can be efficiently utilized, which is
advantageous in further miniaturizing the zoom optical system. In
addition to this advantage, unwanted reflected light between lens
surfaces can be suppressed by cementing the lens elements together.

[0281]In the zoom optical system, preferably, the first lens group may
include a cemented lens element. If the size of the optical system in the
optical axis direction is reduced, decentering error sensitivity in the
first lens group is increased, which may necessitate improvement in
mechanical precision of the lens barrel or adjustment between the lens
elements in the first lens group. In the above arrangement, since the
cemented lens element is included in the first lens group, decentering
error sensitivities of the lens elements in the first lens group can be
remarkably reduced. Even in need of adjustment between the lens elements,
sensitivity balance can be desirably retained. Also, this arrangement
enables to simplify the lens barrel construction of the first lens group.
Accordingly, unlike the conventional arrangement in which a larger space
for the optical system is required because of mechanical constraints
despite an optical disadvantage, the space for the zoom optical system
can be efficiently utilized, which is advantageous in further
miniaturizing the zoom optical system. In addition to this advantage,
unwanted reflected light between lens surfaces can be suppressed by
cementing the lens elements together.

[0282]An imaging lens device according to another aspect of the invention
includes the aforementioned zoom optical system, wherein the zoom optical
system is so configured as to form an optical image of a subject on a
predetermined image forming plane. This arrangement enables to realize a
compact, high-resolution, and zoomable imaging lens device that is
mountable in a mobile phone, a personal digital assistant, or a like
device.

[0283]A digital apparatus according to still another aspect of the
invention includes the aforementioned imaging lens device; an image
sensor for converting the optical image into an electric signal; and a
controller for causing the imaging lens device and the image sensor to
perform at least one of still image shooting and moving image shooting
for the subject, wherein the zoom optical system in the imaging lens
device is mounted in such a manner that the optical image of the subject
is formed on a light receiving surface of the image sensor. Preferably,
the digital apparatus may be a mobile terminal device. These arrangements
enable to realize a digital apparatus loaded with a zoomable imaging lens
device while retaining high-resolution performance. The mobile terminal
device is a digital apparatus which is ordinarily used in a mobile
environment, as represented by a mobile phone, a personal digital
assistant, or a like device.